Method and apparatus for dispensing small volume of liquid, such as with a weting-resistant nozzle

ABSTRACT

A wetting-resistant nozzle for accurately and precisely dispensing small volumes of liquids. The nozzle comprises an internal flowpath, and an external surface that recedes from the discharge point at an angle greater than 90 degrees, and an exceptionally low surface energy for the external surface. The low surface energy material may exist as a coating on top of a shaped substrate. A flat land region may be included and may have sharp edges, one of which may define the boundary of the low surface energy region. Another embodiment includes the low surface energy material as a bulk material through which a hole is drilled. The internal flowpath inside the nozzle may be smoothly tapered. Liquid being dispensed tends not to advance past the edge of the low surface energy region, which may coincide with a geometrically sharp edge. Such nozzles provide improved dispensing of liquids that have both low surface tension and low viscosity, such as organic solvents.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of Provisional ApplicationNo. 60/247,176, filed on Nov. 10, 2000, and Provisional Application No.60/284,783, filed Apr.18, 2001, and Provisional Application No.60/288,025, filed May 1, 2001, each of which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to dispensing liquids in small volumedroplets or narrow diameter jets, and more particularly, to awetting-resistant nozzle capable of dispensing small volume droplets ornarrow diameter jets, wherein the nozzle has a low surface energycoating and/or a nozzle geometry to provide wetting resistance.

[0004] 2. Description of the Related Art

[0005] Dispensing liquids is important in various technologies. Ink-jetprinting is a major application involving the precise dispensing of tinydrops. Another application is three-dimensional printing (3DP), in whichlayers of powder are bound together in by precisely dispensed binderliquid to form three-dimensional objects. Yet another application isdispensing of pharmaceuticals and other liquids for manufacturingmedical devices and dosage forms.

[0006] Dispensing small volume droplets to create printed displays,pharmaceuticals, medical devices and the like, requires precise,predetermined quantities of liquid delivered in precise, predeterminedlocations. One problem currently encountered in dispensing small volumedroplets has been the uncontrolled and inconsistent degree to which thedispensed liquid wets or does not wet the exterior surface of thenozzle. Wetting is undesirable for precision dispensing of liquidsbecause it is a randomizing influence. Ideally, liquid that passesthrough the passageway of the nozzle should be ejected toward the targetas soon as it is dispensed, in a predetermined quantity and directed toa specific location. However, if wetting occurs, a puddle forms at thenozzle exit, and when the liquid from the dispenser enters the puddle itmay or may not immediately exit the puddle because the puddle hasvariable volume. Some or even all of the liquid may go to changing thesize of the puddle rather than being dispensed. Most or all of thepuddle will eventually be ejected as a very large drop, which isespecially undesirable.

[0007] In addition to introducing a randomizing influence on thequantitative dispensing of a liquid, wetting or the presence of a puddlecan effect the direction of dispensed liquid. Misdirection is a changein the angle of the stream, so that the direction of the stream's travelafter leaving the nozzle is different from the direction of thepassageway through the nozzle. Split-streaming occurs when the liquiddispenses as two distinct streams virtually simultaneously. Theseeffects are undesirable in drop-on-demand applications, in which eachdrop is dispensed by directed action of the valve or dispenser, as wellas other forms of dispensing. Another undesirable effect that can alsooccur is called swingback and is described later.

[0008] Typical ink-jet ink has a surface tension of 33 dyne/cm and aviscosity of 8 centiPoise (at room temperature), while water has asurface tension at room temperature of 73 dyne/cm. Achieving non-wettingdispensing becomes increasingly more difficult when dispensing ink belowthe mid-30's for surface tension of the liquid. Current ink-jet printingtechnology uses nozzles with various coatings and designs to printliquids with surface tensions down to the 30's of dyne/cm.

[0009] With traditional ink printing, the ink has been designed to meetthe limitations of the nozzle. For example, for a given nozzle design,the composition of the ink will be engineered and modified withadditives to achieve the performance characteristics required to printwith a given nozzle. Thus, ink compositions are engineered to keepsurface tension and viscosity above certain minimum values, namely, 30'sof dyne/cm. Commercial ink-jet developers have thus avoided designingnozzles for the region of fluid properties that have surface tensionsbelow 30 dyne/cm by developing aqueous based inks that are elaboratelyengineered with combinations of additives.

[0010] Organic solvents have thus been particularly difficult todispense. Organic solvents may have both low surface tension and lowviscosity. The organic solvents of greatest practical interest havesurface tensions in the 20's dyne/cm and viscosity around or less than 1cP. Their low surface tension makes the liquid want to wet or form apuddle at the nozzle exit, and inhibits droplet break off. The viscosityof the liquid helps to pull liquid off of the exit region, overcomingsurface tension and forming drops. If the viscosity is low, the fluidstream may not break into droplets, but instead may stretch and displayrelated problems. This combination makes organic solvents more likelythan water to wet the nozzle during dispensing. Organic solvent areimportant in manufacturing medical products by 3DP because somesubstances of medical interest are soluble only in such solvents, not inwater.

[0011] One consideration in controlling wetting behavior is thegeometric design of the nozzle. The simplest possible nozzle design is asimple orifice, for example, a hole through a large flat surface. Suchnozzles are commonly used in applications such as waterjet cutting andare typically made of sapphire or ruby with a hole drilled through aflat exit surface. These orifices are only available with a flat exitsurface or with a recessed exit. The jewel is typically held in the endof a tube of outside diameter such as 0.050-inch whose edge is typicallycrimped over the edge of the jewel. In applications involving dispensingof drops, such nozzles are prone to wetting because of the flat exitgeometry and the fact that the jewel is not a particularlylow-surface-energy material.

[0012]FIG. 1 illustrates unsatisfactory nozzle performance of a flatexit surface nozzle 100. As shown, a puddle 120 much larger than thedispensed drop 130 forms at the flat exit surface 110. Especially withorganic solvents, such an orifice suffers significantly from wettingwith the establishment of an ongoing puddle that contributes toinconsistent dispensing of the drops. Thus, such flat exit surfacenozzles are not optimal for precision fluid dispensing, especially oforganic solvents.

[0013] Another nozzle currently in use has a sharply tapered cone havingtypically 30 degrees total included angle; an internal passageway with agradual transition of cross-sectional area inside the body of thenozzle, being narrowest at the tip of the nozzle; and a filletedtransition region between the internal passageway and the externalsurface. These nozzles have been typically made for use as wire-bondingtools in the microelectronics industry; thus, the design is not optimalfor limiting the spread of the liquid when printing.

[0014] Some other commercially available nozzles have been made with aflat end (land), and are intended for use as vacuum pick-up tools.Materials from which they are commercially manufactured include tungstencarbide, Delrin™ (an acetal polymer), and alumina (aluminum oxide). Insuch nozzle geometry, particularly the vacuum pick-up tools that areflat-ended, the much-reduced size of tip together with its sharp edgescan help limit the size of the puddle that may form. However, suchgeometry can exhibit another problem, namely, swingback. Swingback isillustrated in FIGS. 2A-2C.

[0015] FIGS. 2A-2C are illustrations of dispensed liquid from acommercially available nozzle illustrated as still frames of video takenat a capture rate of 30 frames per second. The nozzle illustrated inFIGS. 2A-2C were made of Delrin™ an acetal polymer. The liquid beingdispensed was a solution of 40% ethanol, 60% water, and has surfacetension and viscosity closer to the properties of pure ethanol than tothe properties of pure water. The inside diameter of the nozzle orificewas 0.006 inch (152 microns). The exit geometry was a flat cutoff(sharp-edged) as in a vacuum pick-up tool, with the outside diameter ofthe land (flat region) measuring 0.010 inch (254 microns). After thesmall flat land, the nozzle exterior sloped back with a total includedangle of 30 degrees (15 degree half-angle). The direction of dispensingwas vertically downward.

[0016] In FIG. 2A, the stream of liquid 210 is dispensing from thenozzle 220 and the exterior conical surface 205 of the nozzle 220 isdry. In FIG. 2B, the stream of fluid 210 has shut off and a drop ofliquid 230 has swung up onto the conical exterior 205 of the nozzle 220.FIG. 2C illustrates that the swung-back drop of liquid 230 pulls asubsequent stream of fluid off-axis.

[0017] If this sequence is repeated, the swung-back drop on the externalconical surface can grow with incorporation of additional liquid at eachshutoff. The swung-back drop is a source of asymmetry on an otherwisesymmetrical nozzle and it interferes with precise dispensing by causingmisdirection and/or split-streaming. Additionally, the swung-back dropdetaches randomly as a dispensed large drop.

[0018] Dispensed liquid exits the nozzle and moves downward due to bothgravity and momentum from the pressure-driven flow. Liquid has to moveupward in opposition of both the direction of gravity and the directionof the dispensed momentum in order for swingback to occur. The dominantphysical mechanism causing swingback is the surface tension of theliquid.

[0019] Similar nozzles made of tungsten carbide with flat ends weretested and also exhibited results that were unsatisfactory and in somecases, the results were worse. Similar nozzles of polished alumina butwith fillets also exhibited unsatisfactory performance. Polished aluminais believed to be slightly better than Delrin™ as far as surface energy,while the geometry involving fillets is believed to be slightly lessfavorable than the sharp-edged geometry. The filleted geometry ismanufactured because it is useful for wire-bond tools and with aluminait is not possible to manufacture sharp-edged nozzles. Thus, even thoughall of these nozzles have a small-tip externally tapered geometry thatcan be expected to be more advantageous than the nozzle of FIG. 1, whenused with organic solvents they still suffer from wetting or swingback.

[0020] Extensive testing has shown that with many of the organicsolvents of interest, the nozzles made from all of these commerciallyavailable materials still suffer wetting of the outside cone, and inparticular suffer swingback of the last little bit of liquid uponshutoff.

[0021] The literature contains a variety of materials and coatings thathave been developed to attain low surface energy and good non-wettingcharacteristics. A convenient reference point is the well-known materialTeflon™ (polytetrafluoroethylene), which has a surface energy variouslyquoted as 18-22 dyne/cm, most frequently 18 dyne/cm, and has a contactangle with water of 100 degrees. Of materials that are widely known andavailable, Teflon is perhaps the most hydrophobic.

[0022] In Physical Chemistry of Surfaces by Arthur W. Adamson and AliceP. Gast (John Wiley, New York, 1997) p. 356, referencing E. G. Shafrinand W. A. Zisman, J. Phys. Chem., 64, 519 (1960), there is a chartsummarizing hydrophobic polymers by chemical family and by theparticular atomic constitution at the surface. Of the chemical familiesin that chart, fluoropolymers are in general the most hydrophobic. Thesurface constitution —CF₂—, is listed on that chart with a surfaceenergy of 18 dyne/cm and is described as representing Teflon™(polytetrafluoroethylene and related substances). Teflon has asufficiently low surface energy that nozzles made of it alone canperform reasonably well with aqueous solutions. However, even Teflon isnot of sufficiently low surface energy to perform satisfactorily withmost organic solvents.

[0023] In the same chart, the chemical radical with the lowest surfaceenergy is the terminal trifluoromethyl group —CF₃. Zisman concludes thatthe best surface constitution for non-wetting is terminaltrifluoromethyl groups (—CF₃). The radical which is terminal —CF₂Hgroups is not as hydrophobic as terminal trifluoromethyl groups but ismarginally better than the —CF₂— groups which describe Teflon.

[0024] A family of especially low surface energy materials is availablefrom the Cytonix Corporation, Beltsville, Md. The materials aredescribed in U.S. Pat. Nos. 5,853,894 and 6,037,168. These substancesare characterized by having a terminal trifluoromethyl group, and inparticular by having the exposed surface contain a high fraction ofthese terminal trifluoromethyl groups. These are believed to beessentially the lowest surface energy materials known. It is possible toachieve surface energies as low as 10 or even 6 dyne/cm. The mosthydrophobic properties are achieved when the coating has an exposedsurface consisting almost entirely of trifluoromethyl (—CF₃) groups,that is, 100% of the area, with no other substituent groups exposed atthe surface.

[0025] Other nonwetting substances are also listed in these patents. Inparticular, for these materials, it is found that the surface energy islowest on the surface that is exposed to the atmosphere while curing ordrying. At surfaces which were not created during the curing or dryingprocess but rather were exposed later such as by a machining or cuttingoperation, the surface energy is not so low, i.e., the material is notso hydrophobic. Under best conditions, the surface energy achievablewith these fluoropolymers at the cured surface is 6 to 12 dyne/cm.Expressed in terms of contact angle, these substances have reachedcontact angles for water as high as 150 degrees. There are variousformulations including highly fluorinated epoxy (fluoroepoxy), polymerwhich is heat-curable or curable by exposure to ultraviolet light withthe curing causing polymerization, polymer which is already polymerizedand dissolved in a fluorosolvent, resins of varying viscosities, etc.

[0026] Other substances have also been investigated in the literature.While the materials listed below do not have surface energies as low asthat of the Cytonix materials, still they are in most cases morehydrophobic than Teflon. What is listed here is sometimes surface energyor critical surface tension and sometimes, contact angle, whichever isreported in the literature.

[0027] U.S. Pat. Nos. 4,344,993, 4,764,564 and 4,554,325, all titled“Perfluorocarbon based polymeric coatings having low critical surfacetensions,” disclose substances which are modifications ofperfluorocarbon and which have critical surface tension less thanapproximately 14 to 15 dyne/cm, which is described as being lower thanthat of pure perfluorocarbon.

[0028] U.S. Pat. No. 5,426,458 describes a coating of poly-p-xylylene,which is available under the trade name Parylene N and is intended foradhesion resistance and corrosion resistance, having a contact anglewith water of 110 degrees.

[0029] U.S. Pat. No. 5,073,785 comprises applying a coating of amorphousor diamond-like carbon followed by fluorination of this layer, having acontact angle with water of about 105° (100°±5 degrees). U.S. Pat. No.5,900,342 also discloses diamond-like carbon.

[0030] U.S. Pat. No. 4,120,995 achieves a wetting angle for water of105+/−5 degrees that is slightly better than that of Teflon™(polytetrafluoroethylene). Other patents of interest are U.S. Pat. Nos.5,942,317, 4,565,714, and 5,900,342. U.S. Pat. No. 5,736,249 discloses asiliconic polymer having surface energy of 18-21 dyne/cm. The followingU.S. Pat. Nos. are for nozzle plates for ink-jet printing, all in a flatgeometry: 5,812,158 (a low surface energy polymer coating and also acoating of tantalum instead of gold); 5,350,616 (a Kapton film);4,643,948 (coatings for ink jet nozzles, partially fluorinated alkylsilane and a perfluorinated alkane). Other patents for coatings includeU.S. Pat. Nos. 5,608,003; 5,266,222; 4,716,059; 5,942,317; and4,565,714. Efforts have also been made to modify the surface propertiesof silicon for making nozzles, such as in U.S. Pat. No. 4,623,906 whichdiscloses a wetting-resistant coating which transitions from silicon tosilicon nitride to aluminum nitride, but the final surface of aluminumnitride is not adequate to resist wetting by organic solvents.

[0031] There is yet another factor which influences surfacehydrohobicity, namely surface microgeometry. If a surface is made of amaterial that is already hydrophilic, roughness makes it morehydrophilic. Conversely, if a surface is made of a material that isalready hydrophobic, roughness makes it more hydrophobic. This isdescribed in Physical Chemistry of Surfaces by Arthur W. Adamson andAlice P. Gast (John Wiley, New York, 1997) and also in Principles ofColloid and Surface Chemistry, Third Edition, by Paul C. Heimenz and RajRajagopalan, (Marcel Dekker Inc., 1997). Roughness of hydrophobicsurfaces is cited in U.S. Pat. No. 6,037,168, which describes roughhydrophobic surfaces for use in making inexpensive laboratory vessels.

[0032] In addition to these various geometry and surface properties,there is also yet another factor which influences swingback and may besomewhat related to the particular technique used for dispensing. Itappears that the velocity or momentum of the departing liquid also hasan influence on swingback. In particular, under any circumstances andfor any liquid, extremely slow flow is unlikely to break away from thenozzle as a small drop but rather is likely to remain on the nozzle dueto lack of momentum. If dispensing is done through a microvalve and theshutoff of flow of liquid is not abrupt but instead continues graduallyafter nominal shutoff, or if there is any leakage or outflow of fluidbetween commanded dispensings, this can aggravate or cause swingback.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0033]FIG. 1 is an illustration of the operation of a prior art nozzlewith a jewel nozzle opening and flat exit geometry.

[0034]FIG. 2 is an illustration of the operation of a prior art nozzlewith an externally tapered nozzle.

[0035]FIG. 3 illustrates a cross section of one embodiment of a nozzle,the nozzle incorporating a pre-manufactured externally tapered end andan exterior coating in accordance with the principles of the presentinvention.

[0036]FIG. 4 illustrates the surface tangent angle of the nozzle of FIG.3 in accordance with the principles of the present invention.

[0037]FIG. 5 is a photograph of the dispensing end of the nozzle of FIG.3.

[0038] FIGS. 6A-6C show a sequence of operation detailing initial,steady-state, and shut-off flow of ethanol through the nozzle of FIG. 3.

[0039]FIG. 7 shows the electrical waveform applied to the valves inaccordance with the principals of the present invention.

[0040]FIG. 8 illustrates a typical appearance of fluid stream withorganic solvents in response to the waveforms of FIG. 7 in accordancewith the principles of the present invention.

[0041] FIGS. 9A-9C are photographs of roughened and coated nozzles inaccordance with the principles of the present invention.

[0042]FIGS. 10A and 10B show nozzles roughened by laser-machiningcircumferential grooves in accordance with the principles of the presentinvention.

[0043]FIG. 11 shows a nozzle roughened by laser-machining bothcircumferential and slant-height grooves in accordance with theprinciples of the present invention.

[0044]FIG. 12 illustrates one method of applying a coating to a nozzlein accordance with the principles of the present invention.

[0045]FIG. 13 is a schematic view of an apparatus for applying thecoating illustrated in FIG. 12.

[0046] FIGS. 14A-14C illustrate cross sections of various alternategeometries of nozzles in accordance with the principles of the presentinvention.

[0047] FIGS. 15A-15C illustrate a nozzle made of low-surface-energyresin as a bulk material making up the entire tip of the nozzle inaccordance with the principles of the present invention.

[0048] FIGS. 16A-16C illustrate various geometric calculations relatedto FIGS. 15A-15C in accordance with principles of the present invention.

[0049] FIGS. 17A-17G illustrate alternate manufacturing forms of FIGS.15A-15C in accordance with principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0050] A wetting-resistant nozzle, and in particular, an apparatus andcorresponding method for manufacturing a wetting-resistant nozzle foruse in dispensing low surface energy fluids wherein the nozzle includesan exceptionally low surface energy (hydrophobic) coating and specificnozzle geometry, is described in detail herein. In the followingdescription, numerous specific details are provided, such as specificcoatings, specific geometric nozzle configurations, dimensions, specificdispensed fluids, and the like, to provide a thorough understanding ofthe embodiments of the invention. One skilled in the relevant art,however, will recognize that the invention can be practiced without oneor more of the specific details, or with other coatings, dispensedliquids and the like. In other instances, well-known structures oroperations are not shown or not described in detail to avoid obscuringaspects of the invention.

[0051] One embodiment of the present invention includes awetting-resistant nozzle for accurately and precisely dispensing smallvolumes of liquids. The nozzle comprises an internal flowpath, and anexternal surface that recedes from the discharge point at an anglegreater than 90 degrees, and an exceptionally low surface energy for theexternal surface. The low surface energy material may exist as a coatingon top of a shaped substrate. A flat land region may be included and mayhave sharp edges, one of which may define the boundary of the lowsurface energy region. Another embodiment includes the low surfaceenergy material as a bulk material through which a hole is drilled. Inyet another embodiment, the internal flowpath inside the nozzle may besmoothly tapered. Additional aspects such as surface roughening, surfacetangent angles, coatings and geometric configurations are describedherein in more detail with reference to the Figures and Examples.Nozzles in accordance with the principles of the present inventionprovide improved dispensing of liquids that have both low surfacetension and low viscosity, such as organic solvents.

[0052] The nozzle described herein in accordance with aspects of thepresent invention may be axisymmetric having cylindrical symmetry aroundan axis. The axisymmetric external surface may be frusto-conical or itmay be of other curved shape having axisymmetry. The axes of symmetry ofboth the internal flowpath and the external surface may be identical.The nozzle may have a surface tangent angle, as defined for particulartip geometry, which is greater than 90 degrees and perhaps substantiallygreater than 90 degrees.

[0053] The nozzle described herein in accordance with aspects of thepresent invention may be made of a bulk material which is suitable forwhatever manufacturing operations may be desired to produce the desiredgeometry, while its surface attains the desired surface energyproperties in appropriate places by means of a coating of a materialhaving low surface energy. Alternatively, the nozzle may use a lowsurface energy material as a bulk material that is used to makeessentially all of the nozzle tip including its surface.

[0054] Several embodiments of nozzle geometry are defined herein inaccording to the geometric nature of the transition between the flowpassageway and the nozzle exterior. One embodiment of the nozzleincludes a sharp, essentially knife-edge as the transition. Due tomanufacturing limitations it should be considered that any real tipwould have a transition region which is either a finite (non-zero)radius of curvature or a finite (non-zero) width of flat region, but insome circumstances the dimension of the radius of curvature or landwidth may be very small in comparison to the diameter of the orifice,and this can be considered a knife edge. In such a case the detailedshape of the transition region is less important to the final dispensedfluid. For example, manufacturing a knife-edge orifice would be possibleif the orifice diameter were of a moderate size rather than extremelysmall. Appropriate regions of the nozzle would include surfaces of a lowsurface energy.

[0055] Alternative embodiments of nozzles have small diameter orificessuch that, given the manufacturing limitations applicable tomanufacturing the tip, it is not possible to attain the limitingsituation of a knife-edge. In such a case, the nozzle may comprise asmall land that provides minimal space for development of a persistentdrop. A land is a flat region essentially perpendicular to the principalflow direction of the nozzle. A sharp edge at the outer edge of the landmay help to discourage the liquid from advancing beyond that edge, asdoes a receding, possibly tapered (or other-shaped) exterior.Appropriate regions of the nozzles would have a low surface energy. Thenozzles of the first several examples are for the case where a flatsurface is deliberately manufactured at the tip.

[0056] In accordance with yet another embodiment of the presentinvention, there is a nozzle configuration wherein the nozzle exterioris essentially a portion of a sphere, namely, curved, having low surfaceenergy, and then a hole is drilled through the curved material. A fairlysharp corner or edge may be assumed to exist where the hole meets thecurve. Alternatively, nozzles with fillets are also possible, having lowsurface energy in appropriate regions.

[0057] In accordance with another aspect of the invention, anotherconsideration that influences the wetting of a solid by a liquid is thesurface energy of the nozzle surface material, or, more exactly, thecomparison between the values of the surface tension of the liquid andthe surface energy of the solid. Both of these properties are expressedin units of dyne/cm or equivalent units. The surface tension is aproperty of a liquid, which is determined largely by chemistry and canbe significantly influenced by additives (e.g., surfactants). Thesurface energy of a solid is a material property that is determined inlarge part by chemistry but also is influenced to some degree by surfacefinish or microstructure, crystal orientation, manufacturing methods,cleanliness/contaminants, etc. If the solid surface energy is somewhatgreater than the liquid surface tension, by approximately 10 dyne/cm,then wetting typically occurs. If the solid surface energy is somewhatlower than the liquid surface energy, then wetting typically does notoccur. There is a range of partial wetting when the two quantities arein the same range of magnitude as each other.

[0058] In accordance with another aspect of the invention, wetting isalso quantified by the contact angle. The surface contact angle is thetangent angle where the surface of a liquid drop meets the solidsurface. Non-wetting is characterized by liquid droplets “beading up”when they are dispensed onto the solid surface. Contact anglesapproximately equal to or greater than 90 degrees are considerednon-wetting or minimally wetting. Low contact angles of several tens ofdegrees indicate behavior that is almost wetting. At even lower contactangles or greater excess of the surface energy over the surface tension,liquids spread rapidly over the solid surface. Smaller surface energyand larger contact angle are associated with non-wetting behavior. Therelation between solid surface energy, liquid surface tension andcontact angle is known as Young's equation.

[0059] Under aspect of the present invention, various availableformulations of low surface energy materials are discussed herein. Ingeneral, the surface could be made of any material mentioned herein orin the incorporated references which has a surface energy of 17 dyne/cmor smaller (less than that of the commonly available Teflon). Aparticular material which may be used here is a highly fluorinated epoxy(fluoroepoxy). A material that may be used is a material having a largefraction of terminal trifluoromethyl groups at its surface such as isavailable from the Cytonix Corp. Many of these are curable materials,typically heat-curable or curable by application of ultraviolet light.Another version is already polymerized and is dissolved in afluorosolvent for purposes of application, with the fluorosolvent thendisappearing by evaporation (possibly at elevated temperature).

[0060] In particular, for these materials, it is found that the surfaceenergy is lowest on the surface that is exposed to the atmosphere whilecuring or drying, which is associated with the preferred orientation ofthe terminal trifluoromethyl group. At surfaces which are exposed aftercuring or drying, as a result of a machining or cutting operation, thesurface energy is not so low, i.e., the material is not so hydrophobic,which is less favorable for resisting wetting. At surfaces that are cutor otherwise exposed after curing, the surface energy is approximatelyin the range of the surface energy of conventional Teflon. This meansthat design and processing techniques may be arranged so that the finalsurface in the desired parts of the nozzle is an as-cured surface. Oneway of achieving this is to apply the material as a coating on asubstrate that is already in the desired final shape.

[0061] Under best conditions, the surface energy achievable with thesefluoropolymers at the cured surface is 6 to 12 dyne/cm. Expressedalternatively in terms of contact angle, these substances have reachedcontact angles for water as high as 150 degrees. In addition, thefluoroepoxy materials are suitably hard and able to be drilled ifnecessary. The fluoropolymers can also be put onto a surface in a thinlayer and cured to form a coating. They are also immune to organicsolvents of interest including alcohols and chloroform.

[0062] Except where stated otherwise, the data presented herein is fornozzles which have been coated with a Cytonix fluoropolymer FluoroPel™PFC1604A, involving an oligomer with a carbon chain length 5 to 18,which was applied as a liquid resin having a low viscosity similar tothat of water. This substance is already polymerized and is dissolved ina fluorosolvent. In such a case heat is used to evaporate the solventbut heat is not needed for curing (i.e., polymerization). Anotheravailable formulation used for one example is designated GH000 (heatcurable) with the curing causing polymerization. Ultraviolet curingformulations are also available.

[0063] In the data reported here, liquid was dispensed through miniaturesolenoid-operated valves. Fluid was caused to flow through the valveunder action of a steadily maintained pressure from a fluid reservoir.When electric power to the valve is on, the plunger of the valve liftsup from the seat all the way or at least partway. When electrical poweris off, the plunger returns and closes due to the action of a spring andalso fluid pressure. Two sizes or designs of valves were used duringthis work. One type of microvalve had valve seats made of Viton-GF so asto be chloroform-compatible and it was used in experiments involvingchloroform. The other type of valve used in the present work has thesmallest seat size of any standard design currently available. In thiscase the seat was made of EPDM (ethylene propylene diene rubber). Theselatter valves were used with ethanol and ethanol-water mixtures. Alldata reported here were taken with the microvalve being driven by apulse width modulated driving waveform, with a microvalve actuationfrequency of 800 Hz, pulse width approximately 200 microseconds, and avoltage magnitude of pulse of 40 Volts.

[0064] The invention is further described, but is in no way limited, bythe following examples.

EXAMPLE 1 Smooth, Tapered, Coated Nozzle

[0065] In one embodiment of the present invention, the nozzle designincludes several features that together result in an improved wettingresistant nozzle performance. The features of the present embodiment aresummarized in FIG. 3. The overall bulk shape or body of the nozzle ismade of a material which is selected in part for its ability to bemanufactured in the desired shape. The desired surface properties may beobtained by applying a coating to selected places on the nozzle.

[0066]FIG. 3 illustrates one nozzle configuration in accordance with theprinciples of the present invention. The nozzle 300 has an externalsurface 310, an internal passageway or flowpath 320, an inlet 305 and anoutlet 315. The internal flowpath 320 in the present embodiment issmoothly contoured and tapered to allow laminar flow of fluid. Theexternal surface 310 includes a sharply angled exterior surface 330, acoating 340 applied to the external surface 310 between the angledexterior surface 330 and the outlet 315, and a land region 350 at theoutlet 315. The exterior surface 330 may optionally be surface roughenedbefore applying the coating 340. The external surface 310 may beaxisymmetric. The axisymmetric external surface 310 may befrusto-conical as shown in the present embodiment.

[0067] In this example, the transition region between the internalpassageway 320 and an external axisymmetric surface 310 is a small flatregion that is essentially perpendicular to the axis of the internalflowpath 320. This flat region may be referred to as the land 350. Thisgeometry is easier to manufacture than a knife-edge or even a roundedknife-edge, partly because it provides a chance for dimensional errorsto be absorbed simply as irregularity of the dimension of the land. Forexample, if the external surface is highly tapered, minor dimensionalerrors in the coaxiality of alignment of the internal passageway withthe external surface would cause a knife-edge to wander seriously out ofplane or circularity, whereas with the use of a flat land such errorswould merely cause the annular land to have a minor amount ofeccentricity while the land would remain in a well defined plane.Keeping the exit plane perpendicular to the flow direction has moreimpact on flow than keeping the interior edge and the exterior edge ofthe annulus perfectly concentric with each other. Eccentricity of theland has a much less serious impact on dispensing geometry than would bethe impact of a knife-edge wandering out of plane.

[0068] A flat land is defined by where it meets or adjoins two othersurfaces: the internal passageway 320 and the external axisymmetricsurface 310. The angle at which it intersects either of those other twosurfaces is defined as being 90 degrees at the interior, and at theexterior it is less than 90 degrees but can be close to 90 degrees. Itis known that sharp corners or edges, such as where the land meets theexterior, can arrest the spread of a liquid on a surface. Because of theuse of a design with a flat land, the edges where the land adjoins thoseother two features may each be designed to be substantially sharp. Theterm sharp is used with the realization that, at some size scale, anyreal edge has some detail that may approximate a rounded edge having anedge radius. For the present embodiment, a substantially sharp edgemeans that the edge radius may be small compared to the lateraldimension (outer radius minus inner radius) of the land, such as edgeradius being less than one-fifth of the lateral dimension of the land.

[0069] The land 350 is made as small as possible compared to thediameter of the orifice or outlet 315 in order to minimize spaceavailable for a puddle to form. The land is typically a result of aparticular manufacturing process and cannot realistically be of zerowidth, but for purposes of the present embodiment, is minimized.Therefore, for some sets of nozzle dimensions, the land dimension may bedetermined by being the smallest dimension that is practical formanufacturing. An approximate manufacturing limit is believed to be theoutside diameter minus the inside diameter being no smaller thanapproximately 0.001 inch. The nozzles for which experimental results arereported in this example include a small flat land.

[0070]FIG. 3 further illustrates an interior flowpath of the nozzle 300wherein the flowpath includes an angle 380 and a taper 385. The taper385 transitions the internal flowpath from an inlet diameter ID down tothe outlet diameter D of the nozzle at the outlet 315 for dispensing. Agradually tapering internal flowpath 320 helps to achieve a good qualitydispensed flow because it minimizes flow disturbances that might becreated in the flow just before it exits from the orifice. Nozzles havebeen tested which had a more abrupt entrance to the final narrow hole,and these other nozzles had a greater tendency to exhibitsplit-streaming. With the nozzles as shown here, the internal flowpath320 is tapered at an angle typically less than or approximately equal to10 degrees total included angle. The internal flowpath 320 may have aconstant-diameter flowpath for a small distance immediately back fromthe nozzle exit, such as several diameters of the exit hole, and,preceding that, a gradual taper of the described angle.

[0071] In yet another embodiment of the present invention, the surfaceof the internal flowpath or passageway 320 has a relatively largesurface energy, namely, a wettable or hydrophilic surface. Thehydrophilic surface encourages the liquid to occupy an acceptable placein the nozzle, in contrast to the unacceptable presence of liquid on theexternal surface of the nozzle.

[0072]FIG. 4 illustrates surface tangent angle SA for a nozzle 400. Inspecifying a nozzle design, one geometric specification is the surfacetangent angle SA. One ray of this angle is the flow vector that istypically the direction of discharge of flow along the axis of symmetry405 of the flow passageway 410 in the nozzle 400. The other ray is aray, coplanar with the first ray, which goes through the corner wherethe land 415 meets the nozzle external surface 425, and is tangent tothe nozzle external surface 425 at that point. This surface tangentangle SA is greater than 90 degrees, and may be substantially greaterthan 90 degrees. For example, the surface tangent angle SA may be aslarge as 165 degrees or even 170 degrees. In the nozzle 400 shown inFIG. 4, the conical exterior has a total included angle 420 of 30degrees (half-angle 430 being 15 degrees), which means that the externalsurface angle 410 with respect to the flow direction is 165 degrees.

[0073] There is a certain distance back from the tip of the nozzle atwhich the features of the present invention, such as surface tangentangle and surface energy, have an effect. Beyond that distance it is nolonger important to maintain those features of the present invention andit is possible to depart from those features with no adverse impact. Forexample, beyond such distance it is possible to depart from thefrusto-conical shape, and it would also be possible to change to asurface composition or other surface property so as to be not ashydrophobic as in the region near the tip. For example, such a distancewould be related to the largest distance that liquid is capable ofswinging back, or the largest drop that forms if swingback does occur.Such a distance away from the exit may be estimated as 0.5 inch fortypical dimensions of small nozzles for 3DP printing applications.

[0074] In the nozzles of the present embodiment, a sharp corner is wherethe surface properties change from the moderately-wetting orhighly-wetting surface energy of the land to the lower surface energy ofthe hydrophobic external surface. This abrupt physical edge andmaterials change provides two disincentives to the further spread offluid, namely, the sharp change of angle and the change to a much morehydrophobic surface.

[0075] Therefore, the coating procedure is conducted so as to attempt tocause the resin to stop specifically at the sharp comer or edge wherethe conical exterior meets the land, but not to coat the land. If theland is small, it is acceptable for the land to be of a relatively highsurface energy. In fact, as described, the presence of a small land ofrelatively high surface energy may even be helpful in controllingswingback of drops. The land may provide a place for excess fluid tocollect that might otherwise swing back onto the exterior cone. The useof a sharp edge where the land meets the external surface may serve thepurpose of arresting the spread of fluid on a solid; namely, todiscourage liquid on the land from spreading onto the conical exterior.

[0076] The coating material applied to the nozzles of this example wasCytonix FluoroPel PFC 1604A, which is a relatively low viscosityformulation, with heating in accordance with the manufacturer'sinstructions

[0077] The overall bulk shape or body of the nozzle may be made of amaterial that is selected in part for its ability to be manufactured inthe desired shape. Examples of suitable bulk materials include tungstencarbide and also other ceramics, metals, silicon and polymers.Manufacturing processes appropriate to various of these materials forpurposes of making the desired nozzle shape include machining, drilling,various forms of EDM, etching, molding/casting, etc. The desired surfaceproperties may be obtained by applying a coating to selected places onthe nozzle.

[0078] The nozzles of this embodiment were made of tungsten carbide.Tungsten carbide can be manufactured into varied and complex geometriesby sintering powder together. Tungsten carbide can be ground to providefiner resolution and is electrically conductive. The electricconductivity means the tungsten carbide can be cut by ElectricalDischarge Machining so as to make cuts that are accurately dimensioned,sharp-edged and burr-free. Tungsten carbide has a relatively largesurface energy, which is not a useful property for the vast majority ofthe external surface when fluid is being dispensed. Therefore, thenozzles of the present embodiment were coated, such as with the Cytonixmaterial, to provide low surface energy on appropriate surfaces. Havingthe uncoated regions such as the small exposed land and the interior ofthe flow passageway be of relatively large surface energy (hydrophilicor wetting) may be of some use in encouraging the last segment of liquidto remain in those places rather than swinging up onto the exterior conesurface. For example, this surface may have a surface energy of 50dyne/cm or greater.

[0079]FIG. 5 illustrates a nozzle outlet in accordance with theabove-described embodiment. The nozzle is made out of tungsten carbide,and had a coating of fluoropolymer resin applied to its external conicalsurface. The nozzle has a land outside diameter OD of 0.012 inch (305microns), an outlet hole inside diameter ID of 0.0107 inch (272microns), exterior coated with fluoroepoxy. Alternative dimensionsinclude, for example, combinations of orifice diameter and land outsidediameter, respectfully, of: 0.004 inch, 0.005 inch; 0.003 inch, 0.0045inch; 0.002 inch, 0.003 inch; and 0.001 inch, 0.002 inch.

[0080] FIGS. 6A-6C are frames of videos of various flow regimes throughthe nozzle of FIG. 5. The photos in FIGS. 6A-6C are a sequence ofsuccessive frames from a video, taken at around the time of shutoff ofthe programmed sequence of valve pulses. FIG. 6A is a photo of a nozzledispensing a fully-established non-wetting flow of pure ethanol throughthe nozzle. FIGS. 6B and 6C are successive frames of video at a speed of30 frames per second depicting the shutoff sequence of the nozzledispensing the pure ethanol stream. In FIG. 6A, flow is still fullyestablished. In FIG. 6B, a wisp of fluid appears some distancedownstream of the nozzle, but there is no fluid immediately at thenozzle. In FIG. 6C, fluid has stopped flowing out of the nozzle, andwhatever fluid already left the nozzle has fully detached from thenozzle and has left no swingback or drop on the nozzle.

[0081] Videos of flow through the nozzle show that there is a very smallprobability of swingback happening at the time of turning on a stream,and that the most likely time for a drop to swing up and attach to theexterior cone is at the time of shutoff. The present embodimentdescribed herein uses microvalves pulsed at 800 Hz. Programmed operationof the microvalve is intermittent, with approximately 50 consecutivevalve actuations at intervals of 1/800 sec., followed by a somewhatlonger quiet period.

[0082]FIG. 7 illustrates a graph of a typical electrical waveformapplied to a microvalve shown as a Pulse as a function of Time. In thecurrent embodiment, a pulse 710 is sent for a time T₁ to open the valveand begin flow. A period of no pulse or voltage 720 for a period of timeT₂ follows in which the valve is off.

[0083]FIG. 8 illustrates flow from a nozzle pulsed by the waveform ofFIG. 7. During the time that a pulse was being dispensed, the streamappeared to issue from the nozzle 800 as a connected string of bulges810, even though the microvalve was being discretely pulsed, namely,turning on and off repeatedly, being on for a time T₁ of typically 200microseconds followed by off for a time T₂ of typically 1050microseconds. Such discharge is characteristic of fluids of certaincombinations of properties as defined by the Ohnesorge number.

[0084] Experiments in accordance with the present embodiment producedgood coherence of streams issuing from the nozzle. Usually the streamnot only was coherent when it issued from the nozzle but also remainedessentially just as coherent one inch or even several inches below thenozzle. This was due in part to the smooth and very gradually taperinginternal flowpath inside the nozzle.

EXAMPLE 2 Roughness Made by EDM Roughening or Other Random-RoughnessMethods

[0085] Yet another embodiment of the present invention continues to usethe overall geometric features and the hydrophobic materials of thenozzle design of the previous embodiment, while incorporating surfaceroughness, described earlier in very general and brief terms. Ingeneral, this alternative embodiment and those described in thisapplication are substantially similar to previously describedembodiments, and the same reference numbers identifies common elementsand steps. Only significant differences in construction or operation aredescribed in detail.

[0086] The nozzle of the present embodiment takes advantage of thetheoretically predicted increase in apparent hydrophobicity due tosurface roughness by making a surface that is both rough and of lowsurface energy. In the present embodiment, roughening a bulk piece ofhydrophobic material has not done, although it could be done forapplications dispensing relatively easy fluids not requiring the extremelowest surface energies. The reason the bulk piece is not roughened isbecause the leading candidate resins are not as hydrophobic as would bedesired when below-surface material is exposed. Therefore, the nozzlesof this embodiment were produced by making a nozzle body or substratewhich is rough in desired places, and then coating those places with thehydrophobic material of interest in such a way that the final surface ofthe coating also had at least some of the surface roughness features ofthe substrate. In this way the final rough surface was an as-curedsurface having the preferred orientation of molecules at the surface. Inthis example the coating material was the fluoropolymer but it couldalso be any of the other related substances that are discussed herein.

[0087] This nozzle of this embodiment was manufactured by manufacturingthe nozzle with a smooth surface and then roughening the surface in arandom pattern. This example used a form of EDM or spark erosion toroughen the surface of the nozzle. This is possible because the tungstencarbide, of which the nozzle was made, was electrically conductive. Init, the electrode was a closely fitting mating shape which was rotatedwith respect to the nozzle, and as current flowed, sparks at theinterface between the electrode and the nozzle caused erosion of thenozzle. The dimensions of the surface roughness or texture produced bythis process appear to be on the order of single digits of microns.

[0088] After such a rough substrate has been created, the surfacecoating for this embodiment should be such that at least some of thesubstrate roughness is apparent on the coating surface. For example, thecoating thickness dimension must be small enough so as not to fill up orsmooth out the depressions in the patterned or roughened surface.Accordingly, a resin of relatively low viscosity is used. The resin usedwas FluoroPel(™) PFC 1604A from Cytonix Corp. After a coating of thisliquid resin was applied, a jet of compressed gas was directed againstthe coating in a direction away from the tip of the nozzle so as to thinout the coating layer while it is still liquid by pushing some of theliquid to a place where the coating thickness is not important or excessliquid can be removed. After this was done, heating to 60-80 C. wasperformed according to the manufacturer's instructions to evaporate thesolvent or cure the resin.

[0089]FIG. 9A shows a nozzle 900 of the present embodiment as originallymanufactured with a smooth exterior surface 910. In this photograph, thediameter D of the orifice is 0.005 inch (127 microns). FIG. 9B shows thenozzle with a roughened exterior conical surface 920. The roughening isaccomplished by electrical discharge from a rotating closely fittingmating surface (electrode) EDM. The estimated characteristic dimensionof this roughness, average feature-to feature distance, or average depthof roughness, is in the single digit microns. FIG. 9C shows the nozzleof FIG. 9B coated with the described hydrophobic coating 930. Asillustrated, the coating has a sufficiently low viscosity such that theresin does not completely fill up or smooth over the roughness.

[0090] Alternatively, a similar random roughness on the surface byabrasive mechanical means could be created by sandblasting, abrasivewater jet, rubbing with sandpaper or abrasive (which may be selected soas to be harder than the material of the nozzle), and the like. It wouldalso be possible to prepare a rough surface by adding material onto anoriginally manufactured smooth surface, such as by adhering grains ofparticulate matter of a suitable size using a suitable adhesive. In anyof these cases, the coating would then be applied as previouslydescribed.

[0091] Additionally, instead of forming a coating by application ofliquid, it would be possible to use any of the coatings which are knownas being formed by a process amenable to gaseous deposition, such asformation of diamond-like carbon followed by fluorinating by reactionwith a fluorine-containing gas, or the formation of the poly-p-xylylenecoating known as Parylene. Such processes, involving only gaseoussubstances, are adapted to coating minute surface features and veryclosely following the shape of the surface features. These coatingoptions apply as well to the laser-machined examples that follow and ingeneral to any nozzles of the present invention.

EXAMPLE 3 Roughness Made by Laser-Machining, Having PredeterminedGeometry, Circumferential Grooves

[0092] Yet another embodiment of the present invention creates surfaceroughness, in specific predetermined geometries. Removing portions ofthe tungsten carbide material, making grooves or similar relievedfeatures by laser machining, provide the roughening in this embodiment.The method of laser machining used is photoablation/decomposition, whichis said to be superior to melting/evaporation in terms of cuttingquality.

[0093] In accordance with aspects of this embodiment, the positions anddimensions of material that is either removed or left undisturbed can bepredetermined and controlled quite accurately by the programmed positionof the laser beam during the laser machining process. Feature sizes suchas 0.001 inch are possible. It is believed that for structural integrityan appropriate value of the groove-to-groove thickness of remainingmaterial (i.e., distance from the interior machined wall surface of onegroove to the corresponding surface of the adjacent groove) is at leastapproximately 0.0005 inch, for structures manufactured by this method.An appropriate depth of groove is 0.001 inch (25 microns).

[0094] A laser-machined roughness pattern which has been found to workreasonably well for purposes of enhancing wetting resistance is a depthof groove of 0.001 inch (25 microns), a width of groove of 0.001 inch(25 microns), and a remaining wall thickness between grooves of 0.0005inch (13 microns). This results in a situation where only a relativelysmall fraction of the original surface (such as one-third) survivesundisturbed to form high spots, while the rest of the original surfaceis recessed, which is believed to be helpful, Dimensions such as thesehave been used with good results.

[0095] It can be appreciated that if a roughness pattern is going to bemachined into the conical surface by removing material from thatsurface, it is necessary to start with a greater thickness of the landand the nozzle wall than would be used in the non-rough strategy.Sufficient land and wall thickness must be provided to avoid having thelaser-machined grooves puncture into the internal flow passagewaythereby creating leaks. For a groove whose depth is nominally 0.001inch, the bare minimum requirement is that the land outside diameter begreater than the orifice diameter by 0.002 inch (51 microns), in whichcase the bottom of the laser-machined groove would just start to breakthrough into the interior passageway, assuming there were no dimensionalinaccuracy in the groove depth and no eccentricity of the internalflowpath with respect to the nozzle external surface. Practicallyspeaking, some additional amount of material remaining between thebottom of the laser-machined groove and the internal flow passagewaywill remain. Additionally, this material allows for possible dimensionalinaccuracy and eccentricity, in order to avoid puncturing into theinternal flowpath.

[0096] When a groove is laser-machined to a nominal depth of 0.001 inch(25 microns), it is satisfactory to start with a land outside diameterwhich is 0.005 inch greater than orifice inside diameter, leaving anominal wall thickness of 0.0015 inch between the base of the groove andthe internal passageway. This leaves enough of a margin against cuttingtoo deep and puncturing. Slightly smaller margins might also besatisfactory. Of course, for typical nozzle designs, as one goes fartheraway from the tip, the internal flowpath widens less steeply than theexterior of the cone, and so the wall thickness improves as one goesfurther away from the tip.

[0097] After the laser-machining operation, the nozzles may be coatedwith Cytonix PFC 1604A, which is a low viscosity formulation. In orderto thin out the deposited resin and retain as much as possible of theinitially rough topography when the coating process is completed, a jetof clean dusting gas is directed at nozzles just after they are coatedwith liquid resin, in a direction away from the tip. Curing of the resinis then performed according to the manufacturer's instructions.

[0098]FIGS. 10A and 10B illustrate laser machined nozzles. FIG. 10A is aphotograph of a nozzle that has been laser machined in accordance withthe above description. FIG. 10B illustrates the same laser machinednozzle coated with a low viscosity coating.

[0099] In the present embodiment, laser machining has been used here toremove material in predetermined patterns having small featuredimension. However, alternate methods of achieving the same structureincluding photolithography and similar techniques known from themicroelectronics fabrication industry, or even by programmed wire EDMmachining using fine wire. The method of material removal may besomewhat dependent on the selection of the material into which groovesor roughness are being cut. It would also be possible to create surfaceroughness of predetermined geometry by addition of material (such as byadhesion of particles or by vapor deposition or plating) onto aninitially smooth surface rather than by removal of material.

[0100] One parameter for roughness-enhanced hydrophobicity is the ratioof the actual final surface area including all the recesses andprotrusions, compared to the original or projected or flat surface area.The projected surface area is the area that exists, without the surfaceirregularities, when viewed looking normal to the overall surface. Thelarger the ratio of actual surface area to projected surface area, thegreater the improvement in hydrophobicity compared to a flat unmodifiedsurface. There are formulas in the literature of surface science wherethis ratio appears as a parameter. Another way of describing the samephenomena is to imagine that perhaps droplets rest only on peaks, and ifthe area of peaks is small compared to the area of the unmodifiedsurface, then the improvement is substantial. Either way of looking atthe phenomenon provides the same insight as to how to maximize itseffect, namely by making the surface geometry more extreme andirregular.

EXAMPLE 4 Crossed Laser-Machined Grooves

[0101] The preceding example suggested that roughness-enhancedhydrophobicity benefits from a more extreme, irregular surface such asby having only a relatively small fraction of the original surfacesurvive. The previous example accomplished this in a one-dimensionalsense with parallel grooves being created in only one direction, namely,circumferential. There is probably some limitation as to how far thistrend can be carried in a one-dimensional sense, because at some pointthe actual width of the groove might have to become impractically large,such as comparable to the natural dimension of a drop of dispensedliquid.

[0102] Accordingly, yet another embodiment of the present invention isto make this groove effect more pronounced by making intersecting cutsin two approximately orthogonal directions, so that the ridges of thepreceding example become essentially interrupted ridges or, as alimiting case, spikes or bristles.

[0103] Accordingly, nozzles were made with a crossed pattern oflaser-machined grooves machined in two mutually orthogonal directionsrather than just circumferential grooves. The circumferential grooveswere as described in the preceding example, with a groove depth of 0.001inch and a groove width of 0.001 inch and a groove-to-groove spacing orremaining wall thickness of 0.0005 inch. The second group of grooves maybe termed slant-height grooves because they exist on the slant height ofthe cone. They were also 0.001 inch deep and 0.001 inch wide. Thisresulted in a pattern in which the most-elevated remaining features ofthe original conical external surface were islands or interrupted ridgesrather than continuous ridges. The crossed grooves removed a greaterfraction of the original surface by removing material from twodirections instead of just one direction.

[0104] It can be appreciated that if a certain number of slant-heightgrooves, having constant groove width, are designed so as to remove acertain fraction of the circumference of a ridge at the tip of thenozzle, then as the cone becomes wider further from the tip, thefraction of the ridge which is removed will not be as large and thecircumferential dimension of those remaining ridge segments willincrease. Eventually the length of ridge segments will increase to theextent that the fraction of a circumference removed by the slant-heightgrooves may no longer be significant. At this point it may be worthwhileto introduce an additional set of slant-height grooves (such as onegroove between each of the already-described slant-height grooves), thatstart some distance away from the tip of the nozzle where there issufficient room. If necessary, as one goes even further from the tip,yet another set of slant-height grooves can be introduced, and so on.

[0105]FIG. 11 is a photograph of a nozzle having laser-machined groovesin both directions. One set of slant-height grooves begins immediatelyat the tip of the nozzle, and a second set of slant-height groovesbegins some distance away from the nozzle tip where there is sufficientroom for an additional groove. This nozzle in FIG. 11 is not yet coated.The nozzles were then coated with Cytonix resin as described inpreceding examples. The slant-height grooves are shown as being straightlines but could also be curved lines if desired.

EXAMPLE 5 Experimental Results Concerning Swingback

[0106] In accordance with yet another embodiment of the presentinvention, swingback of the nozzle is minimized or eliminated. One wayof comparing the performance of various different nozzles is to listconditions for which each type of nozzle does or does not experienceswingback. As already described, swingback is deposition of some liquidon the tapered exterior surface of a nozzle. Although swingback hasoccasionally been observed to a very minor extent at startup of flow, itis primarily a phenomenon associated with the shutoff of flow.

[0107] Instead of all the dispensed liquid continuing to proceed fromthe nozzle toward the target at the time of shutoff, sometimes the lastlittle bit of liquid to pass through the nozzle does not detach from thenozzle, and does not travel toward the target, and instead ends up onthe outside of the nozzle as a result of a rather large change in thedirection of its motion. This is undesirable because it results in asustained drop on a surface of the nozzle (such as the conical exterior)that is usually asymmetrical and is near enough to the intended exitpath of liquid that it can interact with subsequent dispensed liquid. Asustained drop in that location can pull later exiting liquid away fromits intended path, making for inaccurate direction of travel of liquidand hence inaccurate position of printing. Also a large swung-back dropcan itself detach from the nozzle occasionally at unpredictable timesand fall onto the surface being printed, which might ruin a printedpart.

[0108] Sometimes one shutoff event is enough to produce a largesustained drop on an initially dry nozzle exterior. In othercircumstances, sometimes a sustained drop grows very slowly with eachshutoff event and only becomes a problem after many shutoffs. Unlessotherwise noted in the table, a notation of swingback in this exampleindicates that one shutoff event is sufficient to produce a swingback ofa significant size.

[0109] In Table 1, the vertical axis represents (from top to bottom) asequence of increasing degree of difficulty for liquid to dispense andbreak off cleanly at the end of a commanded flow or series of drops. Theordering of degree of difficulty can perhaps be best understood bythinking in terms of how much momentum the last piece of liquid hascoming out of the nozzle at the time of shutoff, on the thought thatsuch momentum helps to pull or carry the liquid away from the nozzle inopposition to surface tension forces which tend to make it swing up andback. The first case in this axis of the table, which is easiest casefor avoiding swingback, is the case of continuous flow dispensing, alsoknown as line-segment printing. In this case the valve remains opencontinuously for a substantial length of time and so steady-statecontinuous pressure-driven flow exists. In line-segment printing theflowrate and consequently the liquid average velocity is as large as itcan possibly be under given fluid reservoir conditions.

[0110] The next, slightly more difficult case is a pulse train whoselength is a very large number of pulses. In this mode of operation themicrovalve is energized by an electrical waveform having a pulse widththat is about 20% of the duration of one cycle, and then for theremainder of the cycle it is not energized, and this pattern is repeatedfor many consecutive pulses. This is an attempt to produce a fluidstream that is a succession of discrete drops. However, for the organicsolvent liquids used here, the appearance of the dispensed fluid stream,at any distance from the nozzle short enough to be useful in threedimensional printing, is believed to be connected bulges rather thandiscrete individual drops as already described in FIG. 8.

[0111] When the pulse train contains a very large number of consecutivepulses, this means that the situation regarding flow and form of fluidstructures has reached quasi-steady-state and there is no influence ofany possible startup transient which might last for some number ofcycles or pulses. The fluid stream contains an average fluid exitvelocity that is some fraction of what it was in the case ofline-segment printing, somewhat reflecting the fact that the valve isopen for only a fraction of the overall time. In the situation thatexists after a substantial number of consecutive actuations, this(average) exiting velocity is as large as it can possibly be for pulsedoperation.

[0112] Cases of further increasing difficulty are when the number ofpulses in each pulse train is finite and becomes smaller and smaller. Inbetween the described pulse trains are time intervals of sufficientlength that there is no carry-over effect from one pulse train toanother. It has been observed in calibrations of flowrate for pulsedoperation of microvalves that there is a correction factor describingthe fact that the flowrate (during the time that flow is on), or volumeper drop, becomes smaller as the pulse train becomes shorter andshorter. The correction is in the range of 10% to 15% for the shortestpulse trains compared to very long pulse trains. It is believed thatthis correction illustrates the existence of a startup transient at thebeginning of a pulse train, implying that there is less momentumcontained in a short pulse train than in a pulse train that is longenough to have reached quasi-steady-state. This decreased momentum forshorter pulse trains probably also makes for more difficulty as far asclean breakoff of fluid from the nozzle. Of course, for a nozzle to beable to print finely detailed features such as in 3DP, it is desiredthat flow be able to shut off cleanly without swingback even for rathershort numbers of pulses in a pulse train.

[0113] The other axis of the table is a progression of degree ofroughness of the external conical surface of the nozzle, which isfurther elaborated by listing results for two different fluids to alsoillustrate a sort of progression in terms of difficulty of the fluid fornon-wetting purposes. The progression in this axis of the table is basedon the belief that rougher is better, at least for dispensing puresolvents. The first three columns in the table form a progression fromsmooth to slightly rough to rougher. The progression of roughness isfrom a smooth surface to an EDM roughened surface to a surface withlaser-machined grooves in only the circumferential direction. In thelast column of the table, the progression further advances to a surfacewith laser-machined grooves in two mutually orthogonal directions. Allof the surfaces are coated with a low surface energy coating.

[0114] In this table, the first column is for a nozzle whose exteriorwas smooth as purchased, and was coated with Cytonix. The slightlyrougher situation for a nozzle that was EDM-roughened and then coatedwith Cytonix. This surface was somewhat rougher but was not an extremeamount of roughening. The next column was for a still rougher nozzlethat was laser-machined with circumferential grooves and was then coatedwith Cytonix. It was a nozzle of 0.003-inch inside diameter, 0.011-inchland outside diameter, laser-roughened with groove width and ridge widtharound 0.001 inch depth of groove half to 1 thousandth of an inch,coated with Cytonix PFC 1604A (low-viscosity). The crossed groove casein a later column had similar size grooves in the other direction aswell. The crossed-groove design had circumferential grooves dimensionedas 0.001-inch deep and 0.001-inch wide with 0.0005-inch thickness ofwall or remaining material between grooves. The slant-height grooveswere similar with a spacing which permitted the ridge segments to beslightly longer than wide, near the tip of the nozzle, with furtherincreases in segment length further away from the tip. Alllaser-machined nozzles had orifice diameter 0.003-inch (76 microns). Fordata in this table, all nozzles had a total included angle of 30degrees.

[0115] The generally observed ranking of the fluids is that ethanol isan easier fluid and chloroform is a more difficult fluid as far asavoiding wetting. Because of this pattern, one of the better nozzles forethanol is repeated for the more difficult chloroform, and after that isincluded the still rougher design of nozzle having crossedlaser-machined grooves.

[0116] The following table contains the experimental observationsconcerning swingback, reported as observations of conditions that do ordo not result in swingback after repeated shutoff of pulse trains. Thisobservation is of usage which is very closely related to the intendeduse of the nozzles, which is for 3D printing articles such as dosageforms which often include fine printed features having a dimension whichis thin along the fast axis of motion. The table shows how short a pulsetrain can be delivered while remaining free of swingback, which implieshow thin a 3D printed wall or feature would be practical by printingwith such a nozzle.

[0117] The first column or nozzle design (smooth +coated, with ethanol)provided swingback-free shutoff only for line-segment and continuouslypulsed operation. The second column (EDM-roughened +coated, withethanol) provided swingback-free shutoff for line-segment, forcontinuously pulsed and for pulse trains as short as approximately 24consecutive pulses. The third column (laser-machined withcircumferential grooves +coated, with ethanol) provided swingback-freeshutoff for line-segment, for continuously pulsed, and for pulse trainsas short as approximately 4 consecutive pulses, which is just aboutshort enough to be useful for building walls of oral dosage forms. Thus,for these three ethanol cases, the rougher the surface the better is theperformance in resisting swingback.

[0118] The fourth column shows the same nozzle as column 3 but used withchloroform. Compared to column 3, there was degradation of performance,in that swingback-free shutoff with chloroform could only be achievedfor line segment, for continuously pulsed and for pulse trains longerthan approximately 300 consecutive pulses. This is worse than theethanol results, in which swingback-free operation was achieved forpulse trains as short as 4 pulses. With chloroform and these nozzles,pulse trains shorter than 300 pulses resulted in formation of a drop onthe outside of the nozzle. Thus, the further roughening feature ofcrossed grooves was tested with chloroform, and performance improved tobeing able to shut off chloroform swingback-free at a pulse train asshort as 50 pulses. Operation of these nozzles with chloroform atsomewhat less than 50 consecutive pulses did not result in immediateswingback, but after many shutoffs a swung-back drop did develop on theconical surface. In this table, the notation clean means clean breakoffof drops upon shutoff with no swingback, and is the desired state. TABLE1 Performance of nozzles with pure ethanol and pure chloroform Shortdescription of Slightly Moderately Moderately Greatest surface Smoothrough rough rough roughness Liquid Ethanol Ethanol Ethanol ChloroformChloroform Smooth + EDM Laser rough Laser rough Laser rough Cytonixrough + Circumferential + Circumferential + Crossed Cytonix CytonixCytonix grooves + Cytonix Line segment clean clean clean clean cleanContinuously clean clean clean clean clean pulsed Pulse train forms dropclean clean clean clean 300 pulses Pulse train forms drop clean cleanswings back clean 200 pulses Pulse train 50 forms drop clean cleanswings back clean pulses Pulse train 24 forms drop clean clean swingsback swings back pulses Pulse train 6 forms drop slow drop clean swingsback swings back pulses Pulse train 4 forms drop slow drop clean swingsback swings back pulses Pulse train 2 forms drop forms drop swings backswings back swings back pulses

[0119] When all of the entries in this table are taken together, theydefine regions of parameter space in which wetting-free operation can beexpected or should not be expected.

EXAMPLE 6: Nozzle With Complicated Fluid Containing Solute (Smooth,Sharply-Angled Nozzle)

[0120] In accordance with yet another embodiment of the presentinvention, a nozzle for dispensing complicated a fluid-containing soluteis described. The binder liquids that were used in the precedingexamples (ethanol and chloroform) were simple pure solvents that mightbe called prototypical of binder liquids that would be dispensed forpurposes such as manufacturing medical articles. The fact that they arepure solvents means that if any drops or splashes occur and the solventevaporates, nothing is left behind on the surfaces that received thedrops or splashes.

[0121] Binder liquids actually dispensed in the fabrication of medicalproducts by 3DP are likely to have additives dissolved in them thatresult in somewhat different fluid properties. Such binder liquids arelikely to require some amount of additional characterization work. Oneexample of a more complicated binder liquid that has been tried is asolution containing 64% ethanol, 21% water, and 15% triethyl citrate (aplasticizer), having a surface tension of 26 dyne/cm and a viscosity of1 to 2 centiPoise.

[0122] It has been found that for this liquid, roughness of the coatedexterior of the nozzle did not enhance hydrophobicity as it did for puresolvents. For this particular fluid, it has been found that the fluidwet the roughened coated surfaces rather easily, which is a contrast tothe results for pure solvents. For this particular fluid it was found tobe preferable to use a smooth-surfaced, coated nozzle such as wasdescribed in Example 1. In particular, it was found that under thosecircumstances a taper of 20 degrees total included angle for the conicalexternal surface worked better than a taper of 30 degrees. It isbelieved that even smaller total included angles may be even better. Itis also believed that, at least for this family of substances, moredilute solutions are easier than more concentrated solutions as far asdispensing without wetting or swingback. For complicated fluids such asthese, optimum wetting-resistant nozzle design may depend on theconstituents of the fluid and their concentration.

EXAMPLE 7 Nozzle Coating Apparatus

[0123] In accordance with yet another embodiment of the presentinvention, a method and apparatus for coating the nozzles previouslydescribe herein is shown and described. For certain sizes of nozzles, itis possible to apply the coating to the nozzle external surface using anapplicator by hand, possibly while working under magnification. However,improved control of coating placement can be achieved if some sort ofpositioning apparatus is used. Such apparatus may be constructed ofcommercially available optical breadboarding and positioning apparatus.It may include a rotary table for mounting and rotating the nozzle,since the nozzle is axisymmetric, and apparatus such as amultidimensional precision motion stage for positioning an applicator,and may further include a magnifying visual system.

[0124] In applying liquid coatings at dimensions as small as those ofinterest here, an important influence is the behavior of the surface ofa drop of coating resin or liquid in contact with a solid, with theshape and position and motion of the liquid drop showing the influenceof the surface tension of the liquid. The nozzle coating apparatus andtechnique take advantage of the surface-tension-dominated behavior ofliquids involving the advance and recession of small drops on solidsurfaces.

[0125] When a liquid such as a drop contacts a solid surface, there is acontact angle that is determined principally by the relative values ofthe liquid surface tension and the solid surface energy and is describedby Young's Equation. This behavior includes the existence of anadvancing contact angle, for which a drop is on the verge of advancing,and a receding contact angle, for which a drop is on the verge ofreceding. Between these two limiting angles is a range of angles suchthat the contact angle of the liquid on the solid can have any valuebetween these two limiting angles without the position of the liquidedge advancing or receding or changing its position at all.

[0126] This description so far describes the behavior of a drop ofliquid on a flat smooth solid surface. For a geometry which includes asharp convex edge, when a liquid drop reaches the sharp convex comer oredge, it hesitates at the sharp convex corner or edge and the positionof its edge or the extent of its advance is defined by the sharp convexcomer or edge. This behavior has already been described in regard tocontrol of wetting at the nozzle tip, but it is also relevant and usefulfor the positioning of the edge of resin as part of the nozzle coatingprocess. When the edge of a liquid puddle or drop, in this case made ofresin, is at a sharp convex comer or edge, the difference betweencontact angle for advancing past the comer or edge and the contact anglefor receding from the comer or edge can be substantially larger thansimply the difference between the advancing and receding contact angleson a flat surface. This makes it easy to define the edge of an appliedliquid coating by a sharp convex edge. Such hesitation behavior wouldnot be apparent, or would be much less apparent, if an edge were agently curved surface, as opposed to sharply cornered.

[0127] Thus, the geometry of the nozzle itself can be used in definingthe edge of the region upon which the coating is applied, just as thesharpness of the edge together with the change of surface energy(created by the present method) later helps to define the edge of thepossible puddle during dispensing. If the desired position of the edgeof the coating coincides with a sharp edge, then the position of thecoating edge can be largely defined by the as-manufactured sharp edge,with the result that the position of the coating edge becomes far lessdependent on positional accuracy of the applicator, or even the skill ofthe operator, than would be the case if the desired coating edge were ata more ordinary place. This fact allows precision in coating placementand achievement of the desired design of spatial pattern of surfaceenergy, which can help to direct dispensed liquid to remain in certainregions and avoid other regions.

[0128]FIG. 12 illustrates one embodiment of a technique suitable forapplying the low-surface-energy resin to the exterior conical surface ofa nozzle. Steps 1-6 of FIG. 12 can be viewed as steps that are performedat one angular location at a time, or they can be viewed as steps thatare performed as the nozzle surface undergoes rotation around its axisof symmetry.

[0129] Step 1 shows, in cross-section, a bare nozzle 1200 before anycoating is applied. The conical nozzle is shown pointing verticallyupward so that gravity will pull the resin away from the tip.

[0130] Step 2 shows a drop of resin 1210 as it is brought into contactwith the external conical surface 1220 using a small sharp applicator1230 such as a pin. The resin 1210 is brought into contact with theexternal conical surface 1220 a slight distance below the nozzle tip1240.

[0131] Step 3 continues after step 2 and shows that the drop of resin1210 may then be nudged upward by the upward motion of the applicator1230 in a controlled manner. When the drop of resin 1210 reaches thesharp external edge 1240, which is the meeting place of the land 1250and the external surface 1220, it hesitates and forms a slight bulge, astypically occurs due to surface tension when any liquid meets a sharpedge. The applicator 1230 can be moved a slight distance higher than theedge 1240, which insures that the resin 1210 goes all the way to theedge. However, as long as the extra distance is modest, the resin willnot progress past the sharp edge. This behavior of the resin puddle asit is being nudged illustrates that it is quite useful and convenient tohave a sharp external edge, because the hesitation which the edge causesin the spreading of liquid resin provides a sharply-defined edge of theresin-coated region and it is possible to know with quite a degree ofcertainty that the resin has reached all the way to the edge and nofarther.

[0132] Step 4 shows that once contact of resin 1210 all the way to thesharp corner 1240 has been achieved, the applicator 12320 may be broughtback down below the comer, which allows the resin drop 1210 to driftback downward under the influence of gravity. This illustration issimilar to the illustration for Step 2, except that now the resinremains in contact with the conical exterior 1220 of the nozzle 1200 allthe way to the sharp comer 1240. Shortly after this step, the applicator1230 may be removed from contact with the resin 1210.

[0133] Step 5 shows the situation after the applicator 1230 is removed.A layer of resin 1230 hangs downward under the influence of gravity. Forlow viscosity resins this layer would be rather thin, but for highviscosity resins this layer may be thicker. The layer starts at the edgewhere the conical exterior meets the land, and is thicker at lowerelevations. In FIG. 12, the thickness of this layer is exaggerated forpurposes of illustration.

[0134] Step 6 illustrates that if the resin is a relatively viscousheat-curing resin, as the resin becomes warm before actual curing, itsviscosity decreases. This may cause the resin to creep or drip lower onthe nozzle under the influence of gravity, and with the result that thelayer becomes thinner especially near the tip of the nozzle.Nevertheless, the layer never completely disappears from the surfacesthat have been wetted with resin, even those surfaces closest to the tipof the nozzle. Eventually, with a combination of time and temperature,the resin cures and remains in a permanent place and shape. If the resinis such that the exposed as-cured surface has a lower surface energythan the interior of the resin layer, then that will be achieved in thisprocess.

[0135] With any coating liquid and any curing mechanism, while thecoating is still liquid, it is also possible to direct a jet of cleangas at the applied liquid, blowing in a direction away from the nozzletip, to thin the liquid layer by pushing liquid away from the nozzle tipto a place where its thickness does not matter or where it can beremoved from the nozzle. It is estimated that the thickness of the curedcoating at the tip of the nozzle is less than several thousandths of aninch even with the more viscous resin, and well under that dimension forthe low-viscosity resin.

[0136]FIG. 13 illustrates one embodiment of apparatus used to performthe coating operation. The apparatus provides a positioning system foran applicator that is substantially precise, stiff and free of loosenessor backlash. The apparatus may be mounted on a base plate 1310 andincludes a rotary table 1330, which holds the nozzle 1320 being coated.The nozzle 1320 may be a small nozzle with a conical exterior, having anaxis of symmetry 1322, and includes a central hole or orifice 1324 whichmust be kept free of resin. The axis of rotation 1332 of rotary table1330 may coincide with the axis of symmetry 1322 of nozzle 1320 and itsorifice 1324. As shown, the axis of rotation of rotary table 1330 may bevertical and the orientation of the nozzle 1320 may be vertical suchthat gravity pulls the resin away from the orifice 1324, which helps toprevent the orifice 1324 from accidentally becoming filled or blockedwith resin. The rotary table 1330 can be rotated by hand or upon commandas needed, or it can be continuously rotated such as by a motor (notshown), at a suitably slow speed.

[0137] Also mounted onto base plate 1310 is a motion stage 1340,preferably providing three axes of motion, which moves an applicator1350 relative to nozzle 1320. Stage 1340 may comprise three screwmicrometers 1342, 1344 and 1346 in mutually orthogonal directions.Actuators or positioners other than micrometers could also be used, asknown in the fields of motion control and optics.

[0138] As illustrated in FIG. 13, the three directions of motion of thestage 1340 may be vertical and two mutually perpendicular horizontaldirections. However, it also would be possible for one direction ofmotion to be approximately parallel to or tangent to the externalsurface of the axisymmetric surface being coated (i.e., when moving inthe direction parallel to the slant height of a conical nozzle, thedistance of the applicator from the cone surface does not change), andanother direction to be perpendicular to that direction (i.e., purelytoward or away from the conical surface).

[0139] The applicator 1350 that is moved by the stage 1340 may be asolid slender and sharp-pointed such as a pin, which is capable ofmoving an attached drop of resin around on the nozzle 1320. In somecircumstances it may be desirable that the applicator be a hollow tubehaving an interior passageway, which may be pointed or beveled like ahypodermic needle, such that liquid or resin can be delivered throughits interior passageway onto the nozzle 1320.

[0140] In addition to the already described apparatus, the apparatus mayinclude a visual observation system that offers visual magnification toaid in working on small parts. This system may be a purely opticalsystem such as a conventional microscope. The system may include anadjustable magnification (zoom) lens 1360, an electronic camera (notvisible), focusing means 1370 which may be along a vertical axis lookingdown at the coating apparatus, and a display monitor 1362. Imageprocessing software including edge recognition or contrast enhancement,as is known in the art, may be used to process an electronicallyacquired image, possibly in real time, to enhance visualization of theposition of edges of the drop of liquid or resin, such as throughcontrast enhancement and edge detection.

[0141] It has been found that this apparatus can control the placementor position of the actual edge of a puddle of liquid or resin on a smallaxisymmetric work piece, sufficient to routinely and successfully coatthe external conical surfaces of nozzles whose orifice diameter is atleast as small as 25 microns (0.001 inch).

EXAMPLE 8 Various Other Nozzle Shapes

[0142] In accordance with yet another embodiment of the presentinvention, alternative nozzle configurations are described andillustrated. The nozzle shapes described so far, using apre-manufactured shape that has then been coated with a low surfaceenergy coating, have generally been frusto-conical. That is not the onlypossible shape, even for pre-manufactured and coated shapes.

[0143] First of all, the category of knife-edge orifices has alreadybeen mentioned briefly. In a knife-edge orifice, there is a transitionregion between the flow passageway and the extended surface, but thefeatures at the transition region are so small compared to the orificediameter, that the details are unimportant (such as whether thetransition is flat or rounded). This embodiment may be defined as landoutside diameter minus land inside diameter being less than one-tenth ofthe orifice diameter. Although small-diameter nozzles such as 0.003 inchdiameter orifices may not afford that luxury, there could be somenozzles manufactured according to the present invention on asufficiently large size scale, or with an appropriate manufacturingmethod, such that it would be possible to manufacture the orifice edgeas essentially a knife-edge, such as land dimension or radius less than1/10 orifice diameter. In such an event, a low surface energy coatingmay be applied on the external surface up until the knife-edge. Theexternal surface may be conical, curved in either a concave or convexsense, or of other shape. If the external surface is other thanfrusto-conical, the surface tangent angle is as defined in the nextparagraph.

[0144] It is possible that, for nozzles having a flat land, as describedin Example 1, within the region where swingback is possible and nozzledesign features are important, the nozzle external shape could haveaxisymmetric shapes other than frusto-conical, such as curved in eitherthe concave or the convex sense. Curvature of the nozzle externalsurface, as one moves along the slant height, would still fall withinthe scope of the present invention.

[0145] FIGS. 14A-14C illustrate various nozzle shape embodiments alongwith reference of the relevant surface tangent angle SA on eachembodiment. FIG. 14A is a nozzle with an outwardly curving exteriorsurface 1410 and a flat land 1415. The exterior surface tangent angle SAis minimized. FIG. 14B illustrates a nozzle with an inwardly curvingexterior surface 1420 and a flat land 1425. The exterior surface tangentangle SA is greater than in FIG. 14A. FIG. 14C is a nozzle with arelatively flat exterior surface area 1440 and a rounded land 1430,outwardly extending from the internal passageway 1450 of the nozzle. Theland 1430 in FIG. 14C is in the shape of a fillet. Each illustratedembodiment has a surface tangent angle greater than 90 degrees where theexternal shape meets the land. FIG. 14A and 14B illustrate the surfacetangent angle for a nozzle that has a land of finite dimension and thatalso has an external surface which is curved in either a concave orconvex sense, as opposed to being a simple frusto-conical shape.

[0146] It can also be realized that departures from the previouslydescribed nozzle designs are possible at a sufficiently great distancefrom the tip of the nozzle. To the extent that the axisymmetric lowsurface energy exterior is advantageous, it only exerts its advantagewithin a certain distance of the exit. There can be locations that areso far removed from the exit that no drop would ever be able swing upthat far. Accordingly, at such places it is no longer necessary tomaintain the combination of frusto-conical or other axisymmetric shapeand low surface energy. It would be permissible to violate either orboth of those criteria. The distance beyond which swingback could neverreach, and beyond which the stated nozzle design need not be maintained,is not precisely known, but may be estimated as 0.5 inch for typicalorifice and nozzle dimensions of interest for 3DP printing.

[0147] In the descriptions of the shape in previous embodiments, thenozzle has been described as having axisymmetry, which implies that theland is an annulus. While the land may be designed to be an annulushaving its inner and outer circular edges being concentric with eachother, it should be realized that manufacturing imperfections resultingin relative eccentricity of the two circles are permissible.

[0148] With any of these geometric alternatives, roughness could beincorporated such as is described in Examples 2,3 and 4.

[0149] In the examples so far, the low surface energy property has onlybeen provided at the external surface such as frusto-conical surface.The land has not been coated or required to have any particular surfaceenergy. It is possible that the land be left uncoated and haverelatively high surface energy (such as greater than 50 dyne/cm) as hasalready been described in the earliest Examples, displaying the surfaceenergy of the material it is made from, which may be a high surfaceenergy exhibiting hydrophilic behavior.

[0150] Alternatively, it is also possible that the land could bemanufactured to have a small surface energy similar to that of theexternal surface, such as by coating. For example, it is possible tocoat the land with a low surface energy coated just as the externalsurface has been coated. The coating apparatus described in thepreceding example could be used, and the sharp edge where the internalpassageway meets the land could similarly be used to arrest and definethe spread of the coating liquid. The usefulness depends on individualcircumstances such as particular fluid being dispensed.

[0151] Alternatively, nozzles may include fillets. In some instances,the filleted ends seem to be less effective than sharp edges inarresting the spread of liquid or limiting the size of a possible puddleof dispensed liquid, or in defining the edge of a coating. However,there could be cases in which such a filleted nozzle could be useful ifcoated with a low surface energy coating in appropriate places. Such anozzle could also include a flat land region on either side of thefillet, i.e., the fillet could be closer to the fluid passageway orcloser to the external surface, as shown in FIG. 14C.

EXAMPLE 9 Alkyl Ketene Dimer

[0152] In accordance with yet another embodiment of the presentinvention, a coating is applied to the nozzle to increase thewetting-resistant properties of the nozzle. A type of hydrophobicsurface which is hydrophobic as a result of producing a microscopicallyrough surface as it solidifies, is described in “Super-Water-RepellentFractal Surfaces,” by T. Onda, S. Shibuichi, N. Satoh, and K. Tsujii, inLangmuir the ACS Journal of Surfaces and Colloids, Vol. 12 no. 9, May,1996, pages 2125-2127. The material described in this reference isalkylketene dimer (AKD) and is a naturally hydrophobic waxy substancethat produces a pattern of crinkles or cracks as it solidifies from amelted state.

[0153] AKD undergoes fractal growth when it solidifies, although themechanism has not been clarified yet. The paper compares a surfacecontaining this fractal geometry with a surface of the same materialprepared, by cutting, so as to produce an ordinary flat (non-fractal)surface. The conventional (cut) surface had a moderately good contactangle with water of 109 degrees, but, when this material was prepared soas to have a fractal surface, that surface had an extraordinarily largecontact angle with water of 174 degrees. This represents extremehydrophobicity and is far better than the contact angle for any materialnot having this microgeometry.

[0154] AKD could be used as a coating for nozzles instead of thefluoropolymer resin described in the previous embodiments. Thehydrophobicity of this material is dependent on the presence of surfacecracks resembling fractals as it solidifies from liquid. The preparationof the fractal surface in the cited article included heating the AKDmaterial to 90 degrees C. in dry nitrogen and then letting it cool andsolidify. The technique for using this material as a nozzle coatingmaterial could include depositing a thin film of this as liquid on thesubstrate to be coated or treated (the nozzle exterior), at atemperature of around 90 C., and then letting it cool at roomtemperature in the presence of dry nitrogen gas.

[0155] AKD could be applied to the exterior conical surface of a nozzleby essentially the same method and apparatus described in Example 7 forapplying resin, provided that the application of the AKD is carried outat a temperature, such as 90 C., which is suitable for the melting ofAKD. For example, the apparatus that holds the nozzle during applicationof the coating can be heated so as to melt the AKD during times when itis desired to be melted. Heat could also be applied from an externalsource. Solid AKD could be touched to the heated nozzle. The applicatorcould be heated or it does not have to be. When the nozzle is completelycoated with liquid AKD in the desired places, heat could be turned offor down allowing the AKD to solidify in the desired manner.

EXAMPLE 10 Hole Drilled Through Bulk Hardened Fluoropolymer

[0156] Example 10 provides yet another embodiment of the presentinvention. The previous Examples provided an as-cured hydrophobicsurface at the surface of a well-defined external geometry. This wasachieved by manufacturing a base shape having sharp well-definedgeometric features and then applying the low-surface-energy resin as athin coating over the pre-manufactured shape. A different approach,which also provides an effective nozzle for some purposes, is to makethe entire discharge region of the nozzle out of a low-surface-energyresin as a bulk material. In such a case, because a drop of resinnaturally assumes a gently curved shape, it is not likely that one couldachieve such sharply tapered and sharp-edged geometries as in theearlier embodiments, especially given the preference for having thefinal surface be an as-cured surface. Nevertheless, even assuming thatmost surfaces will be gently curved, it is still possible to achievegeometries that are useful for certain fluids and certain purposes.

[0157] This example depends on having a drop of resin fill certain smallopenings or bridge certain small gaps, therefore, the extremely lowviscosity formulation PFC 1 604A from Cytonix has not been used.Instead, the more viscous heat-curable fluoroepoxy resin GH000 fromCytonix has been used. As in previous discussion, this example pertainsespecially to a curable resin that has its lowest surface energy at itsexposed as-cured surface.

[0158] FIGS. 15A-1SC illustrate the dispensing sequence of one suchnozzle. FIGS. 15 illustrate the sequence of manufacturing a nozzle fordispensing a liquid through a tube 1520 having a small body of a curedresin 1510, 1530 at its end, with a hole 1540 through the cured resin.

[0159] The tube may be a metal tube of an inside diameter such as 0.030inch (0.75 mm), which is such that the surface tension of the resin willbe an important factor in the placement and shape of the drop of resinat the end of the tube. When liquid is placed across the end of such asmall diameter tube, the liquid will wick into the tube and will have aninward meniscus at the end. Presumably at the other, hidden surface ofthe resin inside the tube, the resin will also have a similar meniscusthat also wicks onto the wall with a concave curvature.

[0160] One way of manufacturing the desired final geometry is to allow afirst drop 1510 of resin to assume a natural inwardly-curving shape atthe end of the tube, cure it at least partially, as shown in FIG. 15A.Then, deposit a second drop 1530 of resin in the depression formed bythe meniscus, as shown in FIG. 15B. The first drop 1510, being at leastpartially cured, will retain its shape, and provides a resting place forthe second drop 1530, ensuring that the second drop bulges outward asdesired. FIG. 15B illustrates the sequence after the second drop 1530has been deposited. The second drop 1530, assuming an appropriate volumeof resin is deposited, will bulge outward by an amount depending on thevolume of resin deposited, and will cure in that shape, which is aportion of a sphere. This outwardly bulging shape is what is desired andis what is desired to be of low surface energy material. FIG. 15Cillustrates a dispensing hole 1540 in the resin 1510, 1530.

[0161] The first material is not actually required to be low surfaceenergy, and it could be any material that retains its shape afterpartial or full curing because its principal function is to retain itsshape to prevent the second externally bulging drop, which is made oflow-surface-energy material, from wicking in to the tube before itcures. If the first material is identical to the second material, it maybe desirable to only partially cure the material in the first drop justenough so that the material in the first drop becomes highly viscous butstill retains some ability to bond with the next drop, whereas if itwere fully cured the low surface energy of its exposed surface couldmake it difficult for anything else, even the next layer of the samematerial, to stick to the first layer.

[0162] Thus, making the first layer out of a higher surface energy resinmaterial might be useful simply to promote adhesion with both the tubewall and the second drop. In order to enhance adhesion of any resin tothe tube, it may be advantageous to provide a geometric attachmentfeature such that the resin enters the attachment feature, cures and asa result the entire resin plug is mechanically trapped in its desiredlocation at the end of the tube. The attachment feature could forexample, be an internal groove or other indentation on the interior ofthe tube near the end where the resin plug will exist, or small holesthrough the tube wall, roughness on the interior surface of the tube,etc. The extent of curing of heat-curable low-surface-energy fluoroepoxyresin GH000, from Cytonix, is typically observable by color, with theresin turning brown or dark brown when cured.

[0163] As shown in FIG. 15C, a hole is created through the cured resinplug. The hole may be drilled so as to be concentric and coaxial withthe tube. The hole may be made by conventional mechanical drilling,laser drilling, or any other appropriate method. The diameter of thedrilled hole may typically range from 0.007 inch (177 microns) down to0.002 inch (51 microns) or even smaller. This drilling may be performedwith precautions so as to avoid disturbing the exposed as-cured surfaceof the resin adjacent to the hole. Laser drilling may include the use oflasers whose wavelength is in the vacuum ultraviolet range, which isbelieved to be especially well suited for cutting fluoropolymers.

[0164] FIGS. 16A-16C illustrate some geometric relationships whichpertain to the tangency angle at the edge of the hole of FIG. 15C. Theshape of the drop as it is curing is a portion of a sphere having aradius of curvature. How much of a sphere and what is the radius ofcurvature are determined by how much resin is placed there, on thesurface tension of the liquid resin, and on other details. It is assumedthat there is symmetry around the longitudinal axis of the cylindricaltube and the cylindrical hole, i.e., the center of the sphere is on theaxis of the cylindrical hole.

[0165] The angle of interest that effects the droplet breakoff is thelocal tangent angle of the surface SA at the edge of the nozzle exit1610 surface, referenced to the direction of travel of the jet. Thisangle may be termed the surface tangent angle SA. For an ordinary holedrilled perpendicularly through a flat surface, the surface tangentangle is 90 degrees. Surface tangent angles greater than 90 degrees maybe attained by the present invention. The principal variables, labeledin FIGS. 16, are the radius of the hole r_(h), and the radius of thespherical surface r_(s). In all cases illustrated in FIGS. 16, thesurface tangent angle SA is at least slightly greater than 90 degrees.

[0166] In FIG. 16A, the radius of the hole r_(h) is much smaller thanthe radius of curvature of the spherical drop surface r_(S). In thiscase, the surface tangent angle is only slightly greater than 90degrees, perhaps only a few degrees greater than 90 degrees. In FIG.16B, the hole radius r_(h) is about one-quarter of the spherical radiusr_(s), (i.e., r_(h)/r_(s)=0.25), and the surface tangent angle is 104degrees, i.e., about 14 degrees beyond 90 degrees. In FIG. 16C, the holeradius r_(h) is about one-half of the spherical radius r_(s), (i.e.,r_(h)/r_(s)=0.5), and so the surface tangent angle is 120 degrees. Theactual relation between the two radii and the angle is given by

surface tangent angle=90+arcsin (r _(h) /r _(s))

[0167] It can be observed that in FIGS. 16 the flow geometry for flowentering the resin plug with the hole in it includes an abruptcontraction from the inside diameter of the tube to the diameter of thehole. Such an abrupt contraction may be undesirable for at least somefluid flow purposes because it introduces into the fluid flowdisturbances that may show up as irregular flow beyond the nozzle.

[0168] FIGS. 17A-17G illustrate various embodiments that provide asmoothly-tapering interior flowpath 1705 even for this non-coating basedapproach, and also achieves a surface tangent angle SA significantlygreater than 90 degrees just as in the previous FIGS. 16A-16C. Itinvolves creating, such as by machining, a nozzle body 1700 (essentiallya tube) having a smoothly-tapering internal passageway 1705. Then a dropof resin 1720 is applied to the end. A place for application of theresin, such as a recess or pocket 1710, may be provided for thispurpose. Either one-step or two-step application of resin, as before,could be used. The resin could be cured or dried to form alow-surface-energy surface. Finally, a hole 1730 is made through theresin 1720. In FIGS. 17C, 17F and 17G, the diameter of the hole is shownas being essentially equal to the diameter of the lower end of thetapering flowpath in the nozzle body. This results in a smooth internalflowpath without any abrupt change in cross-sectional area. As before,the surface tangent angle at the edge of the hole is determined by theratio of the hole radius to the radius of curvature of the sphericalsurface of the resin drop.

[0169] FIGS. 17A-17F shows a tube whose interior is tapered near thedischarge end just before the resin plug. In the case especially ofsmall diameter orifices, such a tapering avoids the large pressure dropassociated with a long length of small bore, while still not introducingmajor flow disturbance. It also keeps the L/D of the drilled hole withinreasonable range. Most hole manufacturing methods have a limitation onlength to diameter ratio of the hole, and smaller overall size of theresin drop will help to keep the L/D of the drilled hole within areasonable range. The exterior of the pre-manufactured nozzle body inFIGS. 17A-17G can be either straight-sided as shown in FIGS. 17A-17C,17G or tapered as shown in FIGS. 17D-17F.

[0170] If the diameter of the drilled hole is to be particularly small,such as 0.002 inch, or if it is desired that the surface tangent anglebe particularly acute, it may be desirable for the resin region to be ofparticularly small diameter. Smaller size for the resin region willaccentuate the curvature of the resin drop bulging outward.

[0171] Yet another way of making such a nozzle with a hole in it wouldbe to cast a placeholder such as a wire into the resin and then, aftercuring, remove the placeholder such as by etching the wire out. Theplaceholder would have to be of a suitable material such as a metal wiresuch that it could be etched away by an acid that does not damage thecured resin.

[0172] For example, copper wire can be etched away by a solution of hotnitric acid without damaging the fluoroepoxy. When the wire is etchedaway, the hole that remains is of the diameter of the wire. Where thewire enters the drop of resin, there can be expected to be a meniscus bywhich the resin tries to rise up onto the surface of the wire. Thedimensions of this meniscus will be of the same order of magnitude asthe diameter of the wire. The shape of the meniscus may be influenced bywhether the wire was simply inserted into the resin drop or whether thewire was inserted and then withdrawn slightly, because the resin followsthe motion of the wire. When the wire is etched away, the meniscus willremain, and this provides a natural way of making a nozzle having adesirable kind of curvature leading to a sharp edge right at thedischarge. This nozzle shape is shown in FIG. 17G.

[0173] Experiments have been conducted involving discharge of fluid fromnozzles made out of fluoroepoxy, made as illustrated in FIGS. 15A-15Cand drilled with mechanical drills, in both drop-on-demand andcontinuous mode. The flow characteristics with nozzles of the presentembodiment have been significantly better than the flow characteristicsof earlier nozzles made of more conventional materials and designs. Thenozzle of this embodiment, when operating with a solution of propyleneglycol and water in an 80:20 proportion, remained dry in almost alloperating conditions and produced good quality drops.

[0174] Further Discussion

[0175] The nozzles of the present invention could be used to dispensealmost any form of fluid discharge. They could, for example, be used indispensing a continuous jet. By virtue of their physical properties,some liquids, when dispensed intermittently, tend to immediately producediscrete drops, while other liquids dispense as a series of bulgesconnected by narrower strings of liquid. The nozzles of the presentinvention could be used in either case.

[0176] With microvalves, the nozzles of the present invention could beused with both drop-on-demand and line-segment modes of operation.Although the examples have been tested with solenoid-operatedmicrovalves, the nozzles of the present invention could also be usedequally well at the discharge of other types of valves and other typesof dispensers. The nozzles could be used at the discharge of apiezoelectric based drop-on-demand dispenser or fluid ejection system oralso with still other types of dispensers, including boiling(bubble-jet), continuous jet with deflection, and in general, any typeof liquid dispenser. Among the expected benefits of wetting-resistantnozzles would be improved accuracy of drop placement and hence printquality.

[0177] For a piezoelectric dispenser, it may be arranged that when fluidis not being dispensed, the liquid forms a meniscus at the nozzle exitsuch that the meniscus bulges inward, i.e., toward the direction fromwhich the fluid is supplied to the nozzle. This may be achieved bysupplying the fluid from a fluid source that is maintained at a fluidsource pressure, while the dispenser operates in a surrounding gas whichis at atmospheric pressure, wherein the fluid source pressure is atlower than atmospheric pressure. This could for example be attained ifthe fluid source reservoir is open to atmosphere and the liquid surfacelevel in the reservoir is at a lower elevation than the elevation of theexit of the nozzle. This will tend to draw stagnant fluid at the nozzleexit back into the flowpath until the negative pressure of the fluidsupply system corresponds to the negative pressure associated with aninwardly bulging meniscus. This will encourage the last little bit offluid at the nozzle exit, at the time of shutoff, to be drawn back intothe fluid supply system, thereby making that last little bit of fluidless available for swingback. Immediately after shutoff of a dispensingor pulse train, the negative pressure and the tendency toward an inwardmeniscus would help remove fluid from the immediate region of the exitand this would cooperate with the nozzle design features alreadydescribed, which discourage any fluid which does exist at the exit fromswinging back onto the nozzle exterior, to produce a situation which iseven more resistant to wetting and swingback.

[0178] In general, the present invention is defined by the use of asurface that is more non-wetting (lower surface energy) than thecommonly known and used Teflon. The radical describing Teflon is —CF₂—.On the Zisman chart there are two listings with smaller surfaceenergies, namely —CF₂H and —CF₃. Accordingly, a usable coating with thepresent invention could be any coating in which the atomic constitutionat the surface is a monolayer ending in —CF₃, or in —CF₂H or a materialwith a high proportion of such chemical entities at the surface. Anysuch material is an example of a material that could be used in thecurrent invention. Materials described in cited patents, all of whichare incorporated by reference, are examples of materials that could beused.

[0179] Another example of a coating material which could be used, havinga surface energy lower than that of Teflon, is the substance FC721 (alsoFC732) made by the 3M Company, Minneapolis, Minn. (cited in Adamson andin Contact Angles on Hydrophobic Solid Surfaces and TheirInterpretation, by D. Li and A. W. Newmann, Journal of Colloid andInterface Science, vol. 148 No. 1 January 1992 p. 190-200), which is 99%perfluorooctyl methacrylate, with 1% acrylic acid.

[0180] The liquids that could be dispensed through a nozzle of thepresent invention include a very wide variety; essentially any liquidthat has a low enough viscosity to flow through the nozzle sufficientlyquickly. Specifically it includes the category of organic solvents,which includes without limitation alcohols (ethanol, methanol,isopropanol, propanol, and others), chloroform, dichloromethane, otherhalocarbons (including chlorocarbons, fluorocarbons,chlorofluorocarbons, hydrofluorocarbons and other halocarbons), acetone,methylene chloride, ethers (methyl tertiary butyl ether), ethyl acetate,toluene, benzene, dimethyl sulfoxide, N-methyl-2—pyrrolidone, formamide,dimethyl sulfoxide (DMSO), dioxane, acetonitrile, gamma-butyrolactone,propylene carbonate, etc. A list of possible solvents of interest isgiven in the CRC Handbook under “Solvents for Liquid Chromatography.”

[0181] The liquid may also include mixtures or solutions of thesefluids. It can also include liquids which are any organic solventincluding the above named solvents with any additive or additivesdissolved in it. The additive may be either liquid or solid. Examples ofadditives include soluble polymers, polycaprolactone, poly-lactic acid,poly-lactic-co-glycolic acid, propylene glycol, triethyl citrate, etc.The additive could also be any Active Pharmaceutical Ingredient. Theliquid may further comprise solid particles, or colloidal particles ormicelles suspended in it. Nozzles of the present invention could also beused advantageously with water and with aqueous solutions includingpolyacrylic acid (PAA), propylene glycol, etc.

[0182] Nozzles of the present invention could be used other than forthree-dimensional printing, such as for dispensing for high throughputscreening of pharmacological substances. Similarly, such nozzles couldbe used for dispensing of liquids for biological testing, assays, etc.,for medical or veterinary or other general laboratory purposes. Thedispensed liquid could be blood, other bodily fluids, or reagents ordiagnostic substances that are part of the testing. For example, DNAtesting for biological identification, genetic research etc. involvesdispensing of minute quantities of expensive substances.

[0183] Advantages of wetting-resistant nozzles for such applicationsinclude the possibility of using reduced quantities of expensivechemical or biological substances, and reduced likelihood ofcross-contamination. Applications would also exist throughout theprocesses of manufacturing pharmaceuticals, beyond simply dispensing thecompleted pharmaceutical substances into dosage forms.

[0184] A filter may be mounted on each fluid line immediately before thedispenser or printhead, so as to catch particles or debris originatingin any part of the fluid supply system upstream of the filter location.Such a filter may be mounted directly on the printhead.

[0185] The above description of various illustrated embodiments of theinvention is not intended to be exhaustive or to limit the invention tothe precise form disclosed. While specific embodiments of, and examplesfor, the invention are described herein for illustrative purposes,various equivalent modifications are possible within the scope of theinvention, as those skilled in the relevant art will recognize. Theteachings provided herein of the invention can be applied to otherpurposes, other than the examples described above.

[0186] The various embodiments described above can be combined toprovide further embodiments. Aspects of the invention can be modified,if necessary, to employ the process, apparatuses and concepts of thevarious patents, applications and publications described above toprovide yet further embodiments of the invention. All patents, patentapplications and publications cited herein are incorporated by referencein their entirety.

[0187] These and other changes can be made to the invention in light ofthe above detailed description. In general, in the following claims, theterms used should not be construed to limit the invention to thespecific embodiments disclosed in the specification and the claims, butshould be construed to include all devices that operate under the claimsto provide a method for dispensing a liquid. Accordingly, the inventionis not limited by the disclosure, but instead the scope of the inventionis to be determined entirely by the following claims.

I claim:
 1. A nozzle for dispensing a liquid, comprising: a dispenserincluding an internal flow passageway with an inlet and an outlet,wherein liquid exits the dispenser at the outlet; a land adjoining andsurrounding the outlet, the land is substantially perpendicular to alongitudinal axis of the internal flow passageway; and a substantiallyaxisymmetric external surface adjoining and surrounding the land, theexternal surface having a surface tangent angle nearest the land whichis greater than 90 degrees, wherein a surface energy of the externalsurface is less than about 17 dyne/cm.
 2. The nozzle of claim 1, whereinthe substantially axisymmetric external surface is frusto-conical. 3.The nozzle of claim 1, wherein the substantially axisymmetric externalsurface is shaped in a concave curve.
 4. The nozzle of claim 1, whereinthe substantially axisymmetric external surface is shaped in a convexcurve.
 5. The nozzle of claim 1, wherein the internal flow passageway,the land, and the external surface are all substantially axisymmetricaround a common axis.
 6. The nozzle of claim 1, wherein the land has anouter edge that is substantially sharp, and wherein the outer edge isadjacent to the substantially axisymmetric external surface.
 7. Thenozzle of claim 1, wherein the land has an inner edge that issubstantially angular, and wherein the inner edge is adjacent to theinternal flow passageway.
 8. The nozzle of claim 1, wherein the surfacetangent angle nearest the land is greater than or approximately equal to135 degrees.
 9. The nozzle of claim 8, wherein the surface tangent anglenearest the land is greater than or approximately equal to 165 degrees.10. The nozzle of claim 9, wherein the surface tangent angle nearest theland is greater than or approximately equal to 170 degrees.
 11. Thenozzle of claim 10, wherein the surface tangent angle nearest the landis greater than or approximately equal to 175 degrees.
 12. The nozzle ofclaim 1, wherein the land has an outer circular boundary and an innercircular boundary that is substantially concentric with each other. 13.The nozzle of claim 1, wherein the land has an outer circular boundaryand an inner circular boundary that is approximately concentric witheach other.
 14. The nozzle of claim 1, wherein the land has an outsidediameter and an inside diameter, and the outside diameter divided by theinside diameter is less than or approximately equal to
 5. 15. The nozzleof claim 1, wherein the land has an outside diameter and an insidediameter, and the outside diameter divided by the inside diameter isbetween 1.1 and 1.5.
 16. The nozzle of claim 1, wherein the land has aflat land surface energy, and the land surface energy is greater than orequal to about 17 dyne/cm.
 17. The nozzle of claim 1, wherein the landhas a flat land surface energy, and the land surface energy is less thanabout 17 dyne/cm.
 18. The nozzle of claim 1, wherein the internal flowpassageway is tapered, having a cross-sectional flow area that becomessmaller upon progressing from the inlet to the outlet.
 19. The nozzle ofclaim 1, wherein the internal flow passageway has an internal surfacehaving an internal-surface surface-energy, and the internal-surfacesurface-energy is greater than 50 dyne/cm.
 20. The nozzle of claim 1,wherein, at a distance greater than 0.5 inch away from the outlet, theexternal surface changes to a shape different from what it was closer tothe outlet, or changes so as to have a surface energy different fromwhat it had closer to the outlet.
 21. The nozzle of claim 1, wherein thesurface energy of the external surface is less than about 12 dyne/cm.22. The nozzle of claim 1, wherein the surface energy of the externalsurface is less than about 8 dyne/cm.
 23. The nozzle of claim 1, whereinthe external surface is a coating on top of a substrate.
 24. The nozzleof claim 23, wherein the substrate is made of a material selected fromthe group consisting of tungsten carbide, other ceramics, metals,silicon and polymers.
 25. The nozzle of claim 23, wherein the coating isa substance that hardened from liquid after being applied to the nozzle.26. The nozzle of claim 23, wherein the coating cures or hardens from aliquid by heat, by ultraviolet light, by the passage of time since themixing of two components, or by evaporation of a solvent.
 27. The nozzleof claim 23, wherein the coating has a thickness of less than about 50microns.
 28. The nozzle of claim 23, wherein the coating has a lowersurface energy at its surface than it does in its interior.
 29. Thenozzle of claim 23, wherein the coating comprises a fluoropolymer. 30.The nozzle of claim 23, wherein the coating comprises a fluoroepoxy. 31.The nozzle of claim 23, wherein the coating has an exposed surface andthe exposed surface comprises exposed terminal trifluoromethyl radicals.32. The nozzle of claim 30, wherein a majority of the exposed surface isterminal trifluoromethyl radicals.
 33. The nozzle of claim 23, whereinthe coating comprises exposed CF₂H radicals.
 34. The nozzle of claim 23,wherein the coating is applied by gaseous deposition or reaction. 35.The nozzle of claim 23, wherein the coating is selected from the groupconsisting of fluoropolymers, fluoroepoxies, fluorinated diamond-likecarbon, fluorinated amorphous carbon, a siliconic polymer,poly-p-xylylene, tantalum, gold, partially fluorinated alkyl silane,perfluorinated alkane, and perfluorooctyl methacrylate.
 36. The nozzleof claim 23, wherein the coating is a material that solidifies with aplurality of small cracks in its surface, whereby it becomes effectivelymore hydrophobic compared to the same material in a smooth-surfacedcondition.
 37. The nozzle of claim 36, wherein the coating is alkylketene dimer.
 38. The nozzle of claim 1, wherein the external surfacehas a predetermined roughness.
 39. The nozzle of claim 38, wherein theexternal surface has a dimensional scale of roughness that is between 1and 50 microns.
 40. The nozzle of claim 38, wherein the external surfacehas a total surface area and has a projected surface area, and the totalsurface area is more than 1.1 times the projected surface area.
 41. Thenozzle of claim 38, wherein the external surface is a coating on top ofa substrate, and the substrate has roughness.
 42. The nozzle of claim39, wherein the substrate has roughness in a random pattern.
 43. Thenozzle of claim 42, wherein the roughness is produced by spark erosion.44. The nozzle of claim 42, wherein the substrate comprises a collectionof particles.
 45. The nozzle of claim 41, wherein the substrate hasroughness in a prescribed geometric pattern.
 46. The nozzle of claim 45,wherein the pattern comprises circumferential grooves.
 47. The nozzle ofclaim 46, wherein the grooves have a depth of about 0.001 inch and awidth of about 0.001 inch.
 48. The nozzle of claim 46, wherein theexternal surface has a projected surface area of a grooved region andthe grooves in the grooved region occupy a groove area where materialwas removed to make the grooves, and the groove area is more than halfof the projected surface area.
 49. The method of claim 45, wherein thepattern comprises circumferential grooves intersected by slant-heightgrooves.
 50. The nozzle of claim 49, wherein both the circumferentialgrooves and the slant-height grooves have a depth of about 0.001 inchand a width of about 0.001 inch.
 51. The nozzle of claim 50, wherein theexternal surface has a projected surface area of a grooved region andthe grooves in the grooved region occupy a groove area where materialwas removed to make the grooves, and the groove area is more than 60% ofthe projected surface area.
 52. The nozzle of claim 41, wherein thecoating is sufficiently thin that at least some of the substrateroughness appears as the roughness of the external surface.
 53. Thenozzle of claim 41, wherein the coating has a thickness of less thanabout 50 microns.
 54. The nozzle of claim 1 further including adispensed liquid comprising a solvent which is selected from the groupconsisting of ethanol, methanol, isopropanol, other alcohols,chloroform, other fluorocarbons, acetone, methylene chloride, and otherorganic solvents.
 55. The nozzle of claim 1 further including adispensed liquid comprising water or an aqueous solution.
 56. The nozzleof claim 1, further including a dispensed liquid comprising dissolvedsolutes, or insoluble solid particles, or colloidal particles ormicelles suspended in it.
 57. The nozzle of claim 1, further including adispensed liquid comprising an Active Pharmaceutical Ingredient.
 58. Thenozzle of claim 1, further including a dispensed liquid comprising bloodor another bodily fluid, or a reagent or diagnostic substance, or liquidfor three-dimensional printing, or liquid for high throughput screening,or liquid for performing medical or veterinary tests.
 59. The nozzle ofclaim 1, wherein the dispenser is made by coating a substrate, whichprovides the shape of the substantially axisymmetric external surface,on the external surface with a coating having a surface energy less thanabout 17 dyne/cm.
 60. A microvalve-based printhead comprising thedispenser of claim
 1. 61. A piezoelectrically actuated printheadcomprising the dispenser of claim
 1. 62. A bubble-jet printheadcomprising the dispenser of claim
 1. 63. A continuous-jet printheadcomprising the dispenser of claim
 1. 64. A nozzle for dispensing aliquid, comprising: a nozzle having an external surface and an internalpassageway, the internal passageway having a passageway diameter, aninlet and an outlet, the passageway allowing a fluid to flowtherethrough, the external surface and the internal passagewaysubstantially axisymmetric, the external surface having a surfacetangent angle nearest the outlet that is greater than 90 degrees; and atransition region adjoining and surrounding the outlet connecting theexternal surface and the internal passageway, the transition regionhaving an outer diameter and an inner diameter, wherein the outerdiameter minus the inner diameter is less than one-tenth of thepassageway diameter.
 65. The nozzle of claim 64, further including asurface energy of the external surface wherein the surface energy isless than about 17 dyne/cm.
 66. The nozzle of claim 65, wherein thesurface energy of the external surface is less than about 8 dyne/cm. 67.The nozzle of claim 64, wherein the external surface is rough.
 68. Thenozzle of claim 64, wherein the internal flow passageway is tapered,having a cross-sectional flow area that becomes smaller upon progressingin the downstream direction.
 69. A nozzle for dispensing a liquid,comprising: a nozzle having a substantially axisymmetrical internal andan external surface, the internal surface allowing liquid to passtherethrough, the external surface having a surface energy less thanabout 17 dyne/cm and a surface tangent angle from the shared axis thatis greater than 90 degrees.
 70. The nozzle of claim 69, wherein theinternal surface has an inlet and an outlet to form an internal flowpassageway that conducts the liquid along a principal flow direction tothe outlet.
 71. The nozzle of claim 70, wherein the substantiallyaxisymmetric external surface has a surface tangent angle nearest theoutlet that is greater than 135 degrees and the external surface energyis less than about 12 dyne/cm.
 72. The nozzle of claim 69, wherein thesurface energy of the external surface is less than about 8 dyne/cm. 73.The nozzle of claim 69, wherein the external surface is curved.
 74. Thenozzle of claim 69, wherein the external surface is a portion of asphere.
 75. The nozzle of claim 69, wherein the external surface meetsthe flow passageway at an edge that is substantially sharp.
 76. Thenozzle of claim 68, wherein the internal flow passageway is graduallytapered, having a cross-sectional flow area that becomes smaller uponprogressing in the downstream direction.
 77. The nozzle of claim 69,wherein the external surface is formed from a drop of resin.
 78. Thenozzle of claim 69, wherein the nozzle is made by depositing a drop of afirst resin at the end of a hollow tube, curing or partly curing thefirst resin to form a partly cured shape, depositing a drop of a secondresin upon the partly cured shape of the first resin so as to make anoutwardly curving surface, curing both resins, and making a hole throughboth cured resins.
 79. The nozzle of claim 77, wherein the hole is madeby laser drilling or mechanical drilling or by embedding a leachableplaceholder and then leaching out the leachable placeholder.
 80. Thenozzle of claim 77, wherein the drop of second resin has a sphericalshape with a spherical radius, and the hole has a hole radius, and thehole radius divided by the spherical radius is greater than 0.05.
 81. Anozzle for dispensing a liquid, comprising: an internal flow passagewayalong an axis that conducts a liquid along a principal flow directiontoward an exit; a fillet adjoining and surrounding the exit; and asubstantially axisymmetric external surface having a surface tangentangle nearest the fillet which is greater than 90 degrees.
 82. Thenozzle of claim 81, wherein the fillet has a fillet surface energy andthe fillet surface energy is less than about 17 dyne/cm.
 83. The nozzleof claim 81, wherein the fillet has a fillet surface energy and thefillet surface energy is greater than or equal to about 17 dyne/cm. 84.The nozzle of claim 81, further comprising a transition region betweenthe internal flow passageway and the external surface at the exit thatis substantially perpendicular to the principal flow direction.
 85. Amethod of manufacturing a nozzle for dispensing liquid, comprising:manufacturing a nozzle having an internal flow passageway which conductsa liquid along a principal flow direction to an exit, a flat land whichis substantially perpendicular to the principal flow direction, asubstantially axisymmetric external surface having a surface tangentangle nearest the flat land which is greater than 90 degrees; coatingthe external surface; and curing the coating so that it has a surfaceenergy of less than about 17 dyne/cm.
 86. The method of claim 85 furthercomprising, coating the external surface with a liquid coating anddirecting a jet of gas at the coating prior to curing to thin thecoating.
 87. The method of claim 85 further comprising, roughening theexternal surface.
 88. The method of claim 85 wherein the coating isgaseously applied.